Microstructural characteristics of adiabatic shear localization in a metastable beta titanium alloy deformed at high strain rate and elevated temperatures

Energy Technology Data Exchange (ETDEWEB)

Zhan, Hongyi, E-mail: h.zhan@uq.edu.au [Centre for Advanced Materials Processing and Manufacture, School of Mechanical and Mining Engineering, The University of Queensland, St Lucia, Queensland 4072 (Australia); Zeng, Weidong [State Key Laboratory of Solidification Processing, School of Materials, Northwestern Polytechnical University, Xi' an 710072 (China); Wang, Gui [Centre for Advanced Materials Processing and Manufacture, School of Mechanical and Mining Engineering, The University of Queensland, St Lucia, Queensland 4072 (Australia); Defence Material Technology Centre, Level 2, 24 Wakefield St, Hawthorn, VIC 3122 (Australia); Kent, Damon [School of Science and Engineering, University of the Sunshine Coast, Sippy Downs, Queensland 4575 (Australia); Dargusch, Matthew [Centre for Advanced Materials Processing and Manufacture, School of Mechanical and Mining Engineering, The University of Queensland, St Lucia, Queensland 4072 (Australia); Defence Material Technology Centre, Level 2, 24 Wakefield St, Hawthorn, VIC 3122 (Australia)

2015-04-15

The microstructural evolution and grain refinement within adiabatic shear bands in the Ti6554 alloy deformed at high strain rates and elevated temperatures have been characterized using transmission electron microscopy. No stress drops were observed in the corresponding stress–strain curve, indicating that the initiation of adiabatic shear bands does not lead to the loss of load capacity for the Ti6554 alloy. The outer region of the shear bands mainly consists of cell structures bounded by dislocation clusters. Equiaxed subgrains in the core area of the shear band can be evolved from the subdivision of cell structures or reconstruction and transverse segmentation of dislocation clusters. It is proposed that dislocation activity dominates the grain refinement process. The rotational recrystallization mechanism may operate as the kinetic requirements for it are fulfilled. The coexistence of different substructures across the shear bands implies that the microstructural evolution inside the shear bands is not homogeneous and different grain refinement mechanisms may operate simultaneously to refine the structure. - Graphical abstract: Display Omitted - Highlights: • The microstructure within the adiabatic shear band was characterized by TEM. • No stress drops were observed in the corresponding stress–strain curve. • Dislocation activity dominated the grain refinement process. • The kinetic requirements for rotational recrystallization mechanism were fulfilled. • Different grain refinement mechanisms operated simultaneously to refine the structure.

Tuning strain of granular matter by basal assisted Couette shear

Directory of Open Access Journals (Sweden)

Zhao Yiqiu

2017-01-01

Full Text Available We present a novel Couette shear apparatus capable of generating programmable azimuthal strain inside 2D granular matter under Couette shear. The apparatus consists of 21 independently movable concentric rings and two boundary wheels with frictional racks. This makes it possible to quasistatically shear the granular matter not only from the boundaries but also from the bottom. We show that, by specifying the collective motion of wheels and rings, the apparatus successfully generates the desired strain profile inside the sample granular system, which is composed of about 2000 photoelastic disks. The motion and stress of each particle is captured by an imaging system utilizing reflective photoelasticimetry. This apparatus provides a novel method to investigate shear jamming properties of granular matter with different interior strain profiles and unlimited strain amplitudes.

Emergence of coherent localized structures in shear deformations of temperature dependent fluids

KAUST Repository

Katsaounis, Theodoros

2016-11-25

Shear localization occurs in various instances of material instability in solid mechanics and is typically associated with Hadamard-instability for an underlying model. While Hadamard instability indicates the catastrophic growth of oscillations around a mean state, it does not by itself explain the formation of coherent structures typically observed in localization. The latter is a nonlinear effect and its analysis is the main objective of this article. We consider a model that captures the main mechanisms observed in high strain-rate deformation of metals, and describes shear motions of temperature dependent non-Newtonian fluids. For a special dependence of the viscosity on the temperature, we carry out a linearized stability analysis around a base state of uniform shearing solutions, and quantitatively assess the effects of the various mechanisms affecting the problem: thermal softening, momentum diffusion and thermal diffusion. Then, we turn to the nonlinear model, and construct localized states - in the form of similarity solutions - that emerge as coherent structures in the localization process. This justifies a scenario for localization that is proposed on the basis of asymptotic analysis in \\\\cite{KT}.

Emergence of coherent localized structures in shear deformations of temperature dependent fluids

KAUST Repository

Katsaounis, Theodoros; Olivier, Julien; Tzavaras, Athanasios

2016-01-01

Shear localization occurs in various instances of material instability in solid mechanics and is typically associated with Hadamard-instability for an underlying model. While Hadamard instability indicates the catastrophic growth of oscillations around a mean state, it does not by itself explain the formation of coherent structures typically observed in localization. The latter is a nonlinear effect and its analysis is the main objective of this article. We consider a model that captures the main mechanisms observed in high strain-rate deformation of metals, and describes shear motions of temperature dependent non-Newtonian fluids. For a special dependence of the viscosity on the temperature, we carry out a linearized stability analysis around a base state of uniform shearing solutions, and quantitatively assess the effects of the various mechanisms affecting the problem: thermal softening, momentum diffusion and thermal diffusion. Then, we turn to the nonlinear model, and construct localized states - in the form of similarity solutions - that emerge as coherent structures in the localization process. This justifies a scenario for localization that is proposed on the basis of asymptotic analysis in \\cite{KT}.

Strain gradient crystal plasticity effects on flow localization

DEFF Research Database (Denmark)

Borg, Ulrik

2007-01-01

for metals described by the reformulated Fleck-Hutchinson strain gradient plasticity theory. The theory is implemented numerically within a finite element framework using slip rate increments and displacement increments as state variables. The formulation reduces to the classical crystal plasticity theory...... in the absence of strain gradients. The model is used to study the effect of an internal material length scale on the localization of plastic flow in shear bands in a single crystal under plane strain tension. It is shown that the mesh sensitivity is removed when using the nonlocal material model considered...

Signal-to-noise ratio, contrast-to-noise ratio and their trade-offs with resolution in axial-shear strain elastography

International Nuclear Information System (INIS)

Thitaikumar, Arun; Krouskop, Thomas A; Ophir, Jonathan

2007-01-01

In axial-shear strain elastography, the local axial-shear strain resulting from the application of quasi-static axial compression to an inhomogeneous material is imaged. In this paper, we investigated the image quality of the axial-shear strain estimates in terms of the signal-to-noise ratio (SNR asse ) and contrast-to-noise ratio (CNR asse ) using simulations and experiments. Specifically, we investigated the influence of the system parameters (beamwidth, transducer element pitch and bandwidth), signal processing parameters (correlation window length and axial window shift) and mechanical parameters (Young's modulus contrast, applied axial strain) on the SNR asse and CNR asse . The results of the study show that the CNR asse (SNR asse ) is maximum for axial-shear strain values in the range of 0.005-0.03. For the inclusion/background modulus contrast range considered in this study ( asse (SNR asse ) is maximum for applied axial compressive strain values in the range of 0.005%-0.03%. This suggests that the RF data acquired during axial elastography can be used to obtain axial-shear strain elastograms, since this range is typically used in axial elastography as well. The CNR asse (SNR asse ) remains almost constant with an increase in the beamwidth while it increases as the pitch increases. As expected, the axial shift had only a weak influence on the CNR asse (SNR asse ) of the axial-shear strain estimates. We observed that the differential estimates of the axial-shear strain involve a trade-off between the CNR asse (SNR asse ) and the spatial resolution only with respect to pitch and not with respect to signal processing parameters. Simulation studies were performed to confirm such an observation. The results demonstrate a trade-off between CNR asse and the resolution with respect to pitch

Deformation localization at the tips of shear fractures: An analytical approach

Science.gov (United States)

Misra, Santanu

2011-04-01

Mechanical heterogeneities are important features in rocks which trigger deformation localization in brittle, ductile or brittle-ductile modes during deformation. In a recent study Misra et al. (2009) have investigated these different processes of deformation localization at the tips of pre-existing planar shear fractures. The authors identified four mechanisms of deformation, ranging from brittle to ductile, operating at the crack tips. Mechanism A: brittle deformation is the dominant process that forms a pair of long tensile fractures at the two crack tips. Mechanism B: nature of deformation is mixed where the tensile fractures grow to a finite length with incipient plastic deformation at the tips. Mechanism C: mixed mode deformation characterized by dominating macro-scale shear bands, and short, opened-out tensile fissures. Mechanism D: localization of plastic bands in the form of a pair of shear bands at each tip without any discernible brittle fracturing. The transition of the mechanisms is a function of orientation ( α) of the crack with respect to the bulk compression direction and the finite length ( l) of the crack. The aim of this study is to present a theoretical analysis to account for the variability of deformation localization in the vicinity of pre-existing shear cracks considering an elastic-plastic rheological model. The analysis calculates the principal tensile stress ( σ1) and the second stress invariant ( I2) of the stress field at the fracture tip to explain the transition from Mechanism A (tensile fracturing) to Mechanism D (ductile strain). The results show that σ1 at the fracture tip increases non-linearly with increasing α and Ar (aspect ratio of the shear crack), and assumes a large value when α > 50 o, promoting tensile fractures. On the other hand, I2 is a maximum at α < 45°, resulting in nucleation of ductile shear bands.

The plane strain shear fracture of the advanced high strength steels

International Nuclear Information System (INIS)

Sun, Li

2013-01-01

The “shear fracture” which occurs at the high-curvature die radii in the sheet metal forming has been reported to remarkably limit the application of the advanced high strength steels (AHSS) in the automobile industry. However, this unusual fracture behavior generally cannot be predicted by the traditional forming limit diagram (FLD). In this research, a new experimental system was developed in order to simulate the shear fracture, especially at the plane strain state which is the most common state in the auto-industry and difficult to achieve in the lab due to sample size. Furthermore, the system has the capability to operate in a strain rate range from quasi-static state to the industrial forming state. One kinds of AHSS, Quenching-Partitioning (QP) steels have been performed in this test and the results show that the limiting fracture strain is related to the bending ratio and strain rate. The experimental data support that deformation-induced heating is an important cause of “shear fracture” phenomena for AHSS: a deformation-induced quasi-heating caused by smaller bending ratio and high strain rate produce a smaller limiting plane strain and lead a “shear fracture” in the component

Localization and Instability in Sheared Granular Materials: Role of Pore Fluids and Non-monotonic Rate Dependent Rheology

Science.gov (United States)

Ma, X.; Elbanna, A. E.; Kothari, K.

2017-12-01

Fault zone dynamics hold the key to resolving many outstanding geophysical problems including the heat flow paradox, discrepancy between fault static and dynamic strength, and energy partitioning. Most fault zones that generate tectonic events are gouge filled and fluid saturated posing the need for formulating gouge-specific constitutive models that capture spatially heterogeneous compaction and dilation, non-monotonic rate dependence, and transition between localized and distributed deformation. In this presentation, we focus primarily on elucidating microscopic underpinnings for shear banding and stick-slip instabilities in sheared saturated granular materials and explore their implications for earthquake dynamics. We use a non-equilibrium thermodynamics model, the Shear Transformation Zone theory, to investigate the dynamics of strain localization and its connection to stability of sliding in the presence and absence of pore fluids. We also consider the possible influence of self-induced mechanical vibrations as well as the role of external acoustic vibrations as analogue for triggering by a distant event. For the dry case, our results suggest that at low and intermediate strain rates, persistent shear bands develop only in the absence of vibrations. Vibrations tend to fluidize the granular network and de-localize slip at these rates. Stick-slip is only observed for rough grains and it is confined to the shear band. At high strain rates, stick-slip disappears and the different systems exhibit similar stress-slip response. Changing the vibration intensity, duration or time of application alters the system response and may cause long-lasting rheological changes. The presence of pore fluids modifies the stick slip pattern and may lead to both loss and development of slip instability depending on the value of the confining pressure, imposed strain rate and hydraulic parameters. We analyze these observations in terms of possible transitions between rate

The Formation and Evolution of Shear Bands in Plane Strain Compressed Nickel-Base Superalloy

Directory of Open Access Journals (Sweden)

Bin Tang

2018-02-01

Full Text Available The formation and evolution of shear bands in Inconel 718 nickel-base superalloy under plane strain compression was investigated in the present work. It is found that the propagation of shear bands under plane strain compression is more intense in comparison with conventional uniaxial compression. The morphology of shear bands was identified to generally fall into two categories: in “S” shape at severe conditions (low temperatures and high strain rates and “X” shape at mild conditions (high temperatures and low strain rates. However, uniform deformation at the mesoscale without shear bands was also obtained by compressing at 1050 °C/0.001 s−1. By using the finite element method (FEM, the formation mechanism of the shear bands in the present study was explored for the special deformation mode of plane strain compression. Furthermore, the effect of processing parameters, i.e., strain rate and temperature, on the morphology and evolution of shear bands was discussed following a phenomenological approach. The plane strain compression attempt in the present work yields important information for processing parameters optimization and failure prediction under plane strain loading conditions of the Inconel 718 superalloy.

Modeling combined tension-shear failure of ductile materials

International Nuclear Information System (INIS)

Partom, Y

2014-01-01

Failure of ductile materials is usually expressed in terms of effective plastic strain. Ductile materials can fail by two different failure modes, shear failure and tensile failure. Under dynamic loading shear failure has to do with shear localization and formation of adiabatic shear bands. In these bands plastic strain rate is very high, dissipative heating is extensive, and shear strength is lost. Shear localization starts at a certain value of effective plastic strain, when thermal softening overcomes strain hardening. Shear failure is therefore represented in terms of effective plastic strain. On the other hand, tensile failure comes about by void growth under tension. For voids in a tension field there is a threshold state of the remote field for which voids grow spontaneously (cavitation), and the material there fails. Cavitation depends on the remote field stress components and on the flow stress. In this way failure in tension is related to shear strength and to failure in shear. Here we first evaluate the cavitation threshold for different remote field situations, using 2D numerical simulations with a hydro code. We then use the results to compute examples of rate dependent tension-shear failure of a ductile material.

Breast tumor classification using axial shear strain elastography: a feasibility study

International Nuclear Information System (INIS)

Thitaikumar, Arun; Ophir, Jonathan; Mobbs, Louise M; Kraemer-Chant, Christina M; Garra, Brian S

2008-01-01

Recently, the feasibility of visualizing the characteristics of bonding at an inclusion-background boundary using axial-shear strain elastography was demonstrated. In this paper, we report a feasibility study on the utility of the axial-shear strain elastograms in the classification of in vivo breast tumor as being benign or malignant. The study was performed using data sets obtained from 15 benign and 15 malignant cases that were biopsy proven. A total of three independent observers were trained, and their services were utilized for the study. A total of 9 cases were used as training set and the remaining cases were used as testing set. The feature from the axial-shear strain elastogram, namely, the area of the axial-shear region, was extracted by the observers. The observers also outlined the tumor area on the corresponding sonogram, which was used to normalize the area of the axial-shear strain region. There are several observations that can be drawn from the results. First, the result indicates that the observers consistently (∼82% of the cases) noticed the characteristic pattern of the axial-shear strain distribution data as predicted in the previous simulation studies, i.e. alternating regions of positive and negative axial-shear strain values around the tumor-background interface. Second, the analysis of the result suggests that in approximately 57% of the cases in which the observers did not visualize tumor in the sonogram, the elastograms helped them to locate the tumor. Finally, the analysis of the result suggests that for the discriminant feature value of 0.46, the number of unnecessary biopsies could be reduced by 56.3% without compromising on sensitivity and on negative predictive value (NPV). Based on the results in this study, feature values greater than 0.75 appear to be indicative of malignancy, while values less than 0.46 to be indicative of benignity. Feature values between 0.46 and 0.75 may result in an overlap between benign and malignant

Dilatancy of Shear Transformations in a Colloidal Glass

Science.gov (United States)

Lu, Y. Z.; Jiang, M. Q.; Lu, X.; Qin, Z. X.; Huang, Y. J.; Shen, J.

2018-01-01

Shear transformations, as fundamental rearrangement events operating in local regions, hold the key of plastic flow of amorphous solids. Despite their importance, the dynamic features of shear transformations are far from clear, which is the focus of the present study. Here, we use a colloidal glass under shear as the prototype to directly observe the shear-transformation events in real space. By tracing the colloidal-particle rearrangements, we quantitatively determine two basic properties of shear transformations: local shear strain and dilatation (or free volume). It is revealed that the local free volume undergoes a significantly temporary increase prior to shear transformations, eventually leading to a jump of local shear strain. We clearly demonstrate that shear transformations have no memory of the initial free volume of local regions. Instead, their emergence strongly depends on the dilatancy ability of these local regions, i.e., the dynamic creation of free volume. More specifically, the particles processing the high dilatancy ability directly participate in subsequent shear transformations. These results experimentally enrich Argon's statement about the dilatancy nature of shear transformations and also shed insight into the structural origin of amorphous plasticity.

Strain rate measurement by Electronic Speckle Pattern Interferometry: A new look at the strain localization onset

International Nuclear Information System (INIS)

Guelorget, Bruno; Francois, Manuel; Vial-Edwards, Cristian; Montay, Guillaume; Daniel, Laurent; Lu, Jian

2006-01-01

In-plane Electronic Speckle Pattern Interferometry has been successfully used during tensile testing of semi-hard copper sheets in order to measure the strain rate. On one hand, heterogeneity in strain rate field has been found before the maximum of the tensile force (ε t ≅ 19.4 and 25.4%, respectively). Thus, a localization phenomenon occurs before the classic Considere's criterion (dF = 0) for the diffuse neck initiation. On the other hand, strain rate measurement before fracture shows the moment where one of the two slip band systems becomes predominant, then strain concentrates in a small area, the shear band. Uncertainty evaluation has been carried out, which shows a very good accuracy of the total strain and the strain rate measurements

Strain rate measurement by Electronic Speckle Pattern Interferometry: A new look at the strain localization onset

Energy Technology Data Exchange (ETDEWEB)

Guelorget, Bruno [Universite de Technologie de Troyes (UTT), Laboratoire des Systemes Mecaniques et d' ingenierie Simultanee (LASMIS, CNRS FRE 2719), 12 rue Marie Curie, B.P. 2060, 10010 Troyes Cedex (France)]. E-mail: bruno.guelorget@utt.fr; Francois, Manuel [Universite de Technologie de Troyes (UTT), Laboratoire des Systemes Mecaniques et d' ingenierie Simultanee (LASMIS, CNRS FRE 2719), 12 rue Marie Curie, B.P. 2060, 10010 Troyes Cedex (France); Vial-Edwards, Cristian [Departemento de Ingenieria Mecanica y Metalurgica, Pontificia Universidad Catolica de Chile, Vicuna Mackenna 4860, 6904411 Santiago (Chile); Montay, Guillaume [Universite de Technologie de Troyes (UTT), Laboratoire des Systemes Mecaniques et d' ingenierie Simultanee (LASMIS, CNRS FRE 2719), 12 rue Marie Curie, B.P. 2060, 10010 Troyes Cedex (France); Daniel, Laurent [Universite de Technologie de Troyes (UTT), Laboratoire des Systemes Mecaniques et d' ingenierie Simultanee (LASMIS, CNRS FRE 2719), 12 rue Marie Curie, B.P. 2060, 10010 Troyes Cedex (France); Lu, Jian [Universite de Technologie de Troyes (UTT), Laboratoire des Systemes Mecaniques et d' ingenierie Simultanee (LASMIS, CNRS FRE 2719), 12 rue Marie Curie, B.P. 2060, 10010 Troyes Cedex (France)

2006-01-15

In-plane Electronic Speckle Pattern Interferometry has been successfully used during tensile testing of semi-hard copper sheets in order to measure the strain rate. On one hand, heterogeneity in strain rate field has been found before the maximum of the tensile force ({epsilon} {sup t} {approx_equal} 19.4 and 25.4%, respectively). Thus, a localization phenomenon occurs before the classic Considere's criterion (dF = 0) for the diffuse neck initiation. On the other hand, strain rate measurement before fracture shows the moment where one of the two slip band systems becomes predominant, then strain concentrates in a small area, the shear band. Uncertainty evaluation has been carried out, which shows a very good accuracy of the total strain and the strain rate measurements.

Studies of Shear Band Velocity Using Spatially and Temporally Resolved Measurements of Strain During Quasistatic Compression of Bulk Metallic Glass

Energy Technology Data Exchange (ETDEWEB)

Wright, W J; Samale, M; Hufnagel, T; LeBlanc, M; Florando, J

2009-06-15

We have made measurements of the temporal and spatial features of the evolution of strain during the serrated flow of Pd{sub 40}Ni{sub 40}P{sub 20} bulk metallic glass tested under quasistatic, room temperature, uniaxial compression. Strain and load data were acquired at rates of up to 400 kHz using strain gages affixed to all four sides of the specimen and a piezoelectric load cell located near the specimen. Calculation of the displacement rate requires an assumption about the nature of the shear displacement. If one assumes that the entire shear plane displaces simultaneously, the displacement rate is approximately 0.002 m/s. If instead one assumes that the displacement occurs as a localized propagating front, the velocity of the front is approximately 2.8 m/s. In either case, the velocity is orders of magnitude less than the shear wave speed ({approx}2000 m/s). The significance of these measurements for estimates of heating in shear bands is discussed.

Strain Localization and Weakening Processes in Viscously Deforming Rocks: Numerical Modeling Based on Laboratory Torsion Experiments

Science.gov (United States)

Doehmann, M.; Brune, S.; Nardini, L.; Rybacki, E.; Dresen, G.

2017-12-01

Strain localization is an ubiquitous process in earth materials observed over a broad range of scales in space and time. Localized deformation and the formation of shear zones and faults typically involves material softening by various processes, like shear heating and grain size reduction. Numerical modeling enables us to study the complex physical and chemical weakening processes by separating the effect of individual parameters and boundary conditions. Using simple piece-wise linear functions for the parametrization of weakening processes allows studying a system at a chosen (lower) level of complexity (e.g. Cyprych et al., 2016). In this study, we utilize a finite element model to test two weakening laws that reduce the strength of the material depending on either the I) amount of accumulated strain or II) deformational work. Our 2D Cartesian models are benchmarked to single inclusion torsion experiments performed at elevated temperatures of 900 °C and pressures of up to 400 MPa (Rybacki et al., 2014). The experiments were performed on Carrara marble samples containing a weak Solnhofen limestone inclusion at a maximum strain rate of 2.0*10-4 s-1. Our models are designed to reproduce shear deformation of a hollow cylinder equivalent to the laboratory setup, such that material leaving one side of the model in shear direction enters again on the opposite side using periodic boundary conditions. Similar to the laboratory tests, we applied constant strain rate and constant stress boundary conditions.We use our model to investigate the time-dependent distribution of stress and strain and the effect of different parameters. For instance, inclusion rotation is shown to be strongly dependent on the viscosity ratio between matrix and inclusion and stronger ductile weakening increases the localization rate while decreasing shear zone width. The most suitable weakening law for representation of ductile rock is determined by combining the results of parameter tests with

An Experimental Investigation into Failure and Localization Phenomena in the Extension to Shear Fracture Transition in Rock

Science.gov (United States)

Choens, R. C., II; Chester, F. M.; Bauer, S. J.; Flint, G. M.

2014-12-01

Fluid-pressure assisted fracturing can produce mesh and other large, interconnected and complex networks consisting of both extension and shear fractures in various metamorphic, magmatic and tectonic systems. Presently, rock failure criteria for tensile and low-mean compressive stress conditions is poorly defined, although there is accumulating evidence that the transition from extension to shear fracture with increasing mean stress is continuous. We report on the results of experiments designed to document failure criteria, fracture mode, and localization phenomena for several rock types (sandstone, limestone, chalk and marble). Experiments were conducted in triaxial extension using a necked (dogbone) geometry to achieve mixed tension and compression stress states with local component-strain measurements in the failure region. The failure envelope for all rock types is similar, but are poorly described using Griffith or modified Griffith (Coulomb or other) failure criteria. Notably, the mode of fracture changes systematically from pure extension to shear with increase in compressive mean stress and display a continuous change in fracture orientation with respect to principal stress axes. Differential stress and inelastic strain show a systematic increase with increasing mean stress, whereas the axial stress decreases before increasing with increasing mean stress. The stress and strain data are used to analyze elastic and plastic strains leading to failure and compare the experimental results to predictions for localization using constitutive models incorporating on bifurcation theory. Although models are able to describe the stability behavior and onset of localization qualitatively, the models are unable to predict fracture type or orientation. Constitutive models using single or multiple yield surfaces are unable to predict the experimental results, reflecting the difficulty in capturing the changing micromechanisms from extension to shear failure. Sandia

Adiabatic shear localization in a near beta Ti–5Al–5Mo–5 V–1Cr–1Fe alloy

Energy Technology Data Exchange (ETDEWEB)

Wang, Bingfeng, E-mail: biw009@ucsd.edu [School of Materials Science and Engineering, Central South University, Changsha 410083, Hunan (China); Key Lab of Nonferrous Materials, Ministry of Education, Central South University, Changsha 410083, Hunan (China); Department of Mechanical and Aerospace Engineering, University of California, San Diego (United States); Sun, Jieying; Wang, Xiaoyan; Fu, Ao [School of Materials Science and Engineering, Central South University, Changsha 410083, Hunan (China)

2015-07-15

Adiabatic shear localization plays an important role in the deformation and failure of near beta Ti–5Al–5Mo–5 V–1Cr–1Fe alloy used in aircraft's gear at high rate deformation. Hat shaped specimens with different nominal shear strains are used to induce the formation of an adiabatic shear band under controlled shock-loading experiments. When the nominal shear strain is about 0.68, unstable shear deformation of the alloy emerges after the true flow stress reaches 1100 MPa, the first vibration peak during the split Hopkinson pressure bar testing, and the whole process lasts about 62 μs. The microstructures within the shear band in the Ti–5Al–5Mo–5V–1Cr–1Fe alloy are investigated by means of optical microscopy, scanning electron microscopy and transmission electron microscopy. Phase transformation occurs in the shear band when the nominal shear strain increases to 0.68. A number of equiaxed grains with sizes 50–200 nm and alpha″-phase are in the center of the shear band. Kinetic calculations indicate that during the deformation process, the recrystallized nanosized grains can be formed in the shear band by way of the subgrain boundaries rotation, and the alpha″ phase transformation start after the subgrain boundaries rotated to 30°.

Effect of bone-soft tissue friction on ultrasound axial shear strain elastography.

Science.gov (United States)

Tang, Songyuan; Chaudhry, Anuj; Kim, Namhee; Reddy, J N; Righetti, Raffaella

2017-07-12

Bone-soft tissue friction is an important factor affecting several musculoskeletal disorders, frictional syndromes and the ability of a bone fracture to heal. However, this parameter is difficult to determine using non-invasive imaging modalities, especially in clinical settings. Ultrasound axial shear strain elastography is a non-invasive imaging modality that has been used in the recent past to estimate the bonding between different tissue layers. As most elastography methods, axial shear strain elastography is primarily used in soft tissues. More recently, this technique has been proposed to assess the bone-soft tissue interface. In this paper, we investigate the effect of a variation in bone-soft tissue friction coefficient in the resulting axial shear strain elastograms. Finite element poroelastic models of bone specimens exhibiting different bone-soft tissue friction coefficients were created and mechanically analyzed. These models were then imported to an ultrasound elastography simulation module to assess the presence of axial shear strain patterns. In vitro experiments were performed to corroborate selected simulation results. The results of this study show that the normalized axial shear strain estimated at the bone-soft tissue interface is statistically correlated to the bone-soft tissue coefficient of friction. This information may prove useful to better interpret ultrasound elastography results obtained in bone-related applications and, possibly, monitor bone healing.

Falling balls and simple shearing strain

International Nuclear Information System (INIS)

Brun, J L; Pacheco, A F

2006-01-01

The problem of particles falling under gravity allows us to relate Hamiltonian mechanics to such different subjects as elasticity and fluid mechanics. It is with this in mind that mechanics gives us the opportunity of introducing, in a rather simple and unusual form, some concepts such as vorticity, the incompressibility condition or simple shear strain to physics students at the undergraduate level

A Shear Strain Route Dependency of Martensite Formation in 316L Stainless Steel.

Science.gov (United States)

Kang, Suk Hoon; Kim, Tae Kyu; Jang, Jinsung; Oh, Kyu Hwan

2015-06-01

In this study, the effect of simple shearing on microstructure evolution and mechanical properties of 316L austenitic stainless steel were investigated. Two different shear strain routes were obtained by twisting cylindrical specimens in the forward and backward directions. The strain-induced martensite phase was effectively obtained by alteration of the routes. Formation of the martensite phase clearly resulted in significant hardening of the steel. Grain-size reduction and strain-induced martensitic transformation within the deformed structures of the strained specimens were characterized by scanning electron microscopy - electron back-scattered diffraction, X-ray diffraction, and the TEM-ASTAR (transmission electron microscopy - analytical scanning transmission atomic resolution, automatic crystal orientation/phase mapping for TEM) system. Significant numbers of twin networks were formed by alteration of the shear strain routes, and the martensite phases were nucleated at the twin interfaces.

Capturing strain localization behind a geosynthetic-reinforced soil wall

Science.gov (United States)

Lai, Timothy Y.; Borja, Ronaldo I.; Duvernay, Blaise G.; Meehan, Richard L.

2003-04-01

This paper presents the results of finite element (FE) analyses of shear strain localization that occurred in cohesionless soils supported by a geosynthetic-reinforced retaining wall. The innovative aspects of the analyses include capturing of the localized deformation and the accompanying collapse mechanism using a recently developed embedded strong discontinuity model. The case study analysed, reported in previous publications, consists of a 3.5-m tall, full-scale reinforced wall model deforming in plane strain and loaded by surcharge at the surface to failure. Results of the analysis suggest strain localization developing from the toe of the wall and propagating upward to the ground surface, forming a curved failure surface. This is in agreement with a well-documented failure mechanism experienced by the physical wall model showing internal failure surfaces developing behind the wall as a result of the surface loading. Important features of the analyses include mesh sensitivity studies and a comparison of the localization properties predicted by different pre-localization constitutive models, including a family of three-invariant elastoplastic constitutive models appropriate for frictional/dilatant materials. Results of the analysis demonstrate the potential of the enhanced FE method for capturing a collapse mechanism characterized by the presence of a failure, or slip, surface through earthen materials.

Effects of relative density and accumulated shear strain on post-liquefaction residual deformation

Directory of Open Access Journals (Sweden)

J. Kim

2013-10-01

Full Text Available The damage caused by liquefaction, which occurs following an earthquake, is usually because of settlement and lateral spreading. Generally, the evaluation of liquefaction has been centered on settlement, that is, residual volumetric strain. However, in actual soil, residual shear and residual volumetric deformations occur simultaneously after an earthquake. Therefore, the simultaneous evaluation of the two phenomena and the clarification of their relationship are likely to evaluate post-liquefaction soil behaviors more accurately. Hence, a quantitative evaluation of post-liquefaction damage will also be possible. In this study, the effects of relative density and accumulated shear strain on post-liquefaction residual deformations were reviewed through a series of lateral constrained-control hollow cylindrical torsion tests under undrained conditions. In order to identify the relationship between residual shear and residual volumetric strains, this study proposed a new test method that integrates monotonic loading after cyclic loading, and K0-drain after cyclic loading – in other words, the combination of cyclic loading, monotonic loading, and the K0 drain. In addition, a control that maintained the lateral constrained condition across all the processes of consolidation, cyclic loading, monotonic loading, and drainage was used to reproduce the anisotropy of in situ ground. This lateral constrain control was performed by controlling the axial strain, based on the assumption that under undrained conditions, axial and lateral strains occur simultaneously, and unless axial strain occurs, lateral strain does not occur. The test results confirmed that the recovery of effective stresses, which occur during monotonic loading and drainage after cyclic loading, respectively, result from mutually different structural restoration characteristics. In addition, in the ranges of 40–60% relative density and 50–100% accumulated shear strain, relative

Reduced thoracolumbar fascia shear strain in human chronic low back pain

Directory of Open Access Journals (Sweden)

Konofagou Elisa E

2011-09-01

Full Text Available Abstract Background The role played by the thoracolumbar fascia in chronic low back pain (LBP is poorly understood. The thoracolumbar fascia is composed of dense connective tissue layers separated by layers of loose connective tissue that normally allow the dense layers to glide past one another during trunk motion. The goal of this study was to quantify shear plane motion within the thoracolumbar fascia using ultrasound elasticity imaging in human subjects with and without chronic low back pain (LBP. Methods We tested 121 human subjects, 50 without LBP and 71 with LBP of greater than 12 months duration. In each subject, an ultrasound cine-recording was acquired on the right and left sides of the back during passive trunk flexion using a motorized articulated table with the hinge point of the table at L4-5 and the ultrasound probe located longitudinally 2 cm lateral to the midline at the level of the L2-3 interspace. Tissue displacement within the thoracolumbar fascia was calculated using cross correlation techniques and shear strain was derived from this displacement data. Additional measures included standard range of motion and physical performance evaluations as well as ultrasound measurement of perimuscular connective tissue thickness and echogenicity. Results Thoracolumbar fascia shear strain was reduced in the LBP group compared with the No-LBP group (56.4% ± 3.1% vs. 70.2% ± 3.6% respectively, p Conclusion Thoracolumbar fascia shear strain was ~20% lower in human subjects with chronic low back pain. This reduction of shear plane motion may be due to abnormal trunk movement patterns and/or intrinsic connective tissue pathology. There appears to be some sex-related differences in thoracolumbar fascia shear strain that may also play a role in altered connective tissue function.

Effects of different aging statuses and strain rate on the adiabatic shear susceptibility of 2195 aluminum–lithium alloy

International Nuclear Information System (INIS)

Yang, Y.; Tan, G.Y.; Chen, P.X.; Zhang, Q.M.

2012-01-01

The adiabatic shear susceptibility of 2195 aluminum–lithium alloy was investigated by means of split Hopkinson pressure bar. The stress collapse in true stress–true strain curves and true stress–time curves was observed. The adiabatic shear susceptibility of different aging statuses and strain rate were discussed by means of metallography observation. The critical strain, stress collapse time and formation energy of adiabatic shear bands were compared. The results show that different aging statuses and strain rate have significant influences on adiabatic shear behaviors of 2195 aluminum–lithium alloy. The peak-aged specimen has the highest adiabatic shearing susceptibility, while the under-aged specimen has the least adiabatic shear susceptibility. The susceptibility of adiabatic shearing increases with the increases of strain rate.

Effects of different aging statuses and strain rate on the adiabatic shear susceptibility of 2195 aluminum-lithium alloy

Energy Technology Data Exchange (ETDEWEB)

Yang, Y. [School of Materials Science and Engineering, Central South University, Changsha 410083, Hunan (China); State Key Laboratory of Explosion Science and Technology, Beijing 100081 (China); Tan, G.Y., E-mail: yangyanggroup@163.com [School of Materials Science and Engineering, Central South University, Changsha 410083, Hunan (China); Chen, P.X. [School of Materials Science and Engineering, Central South University, Changsha 410083, Hunan (China); Zhang, Q.M. [State Key Laboratory of Explosion Science and Technology, Beijing 100081 (China)

2012-06-01

The adiabatic shear susceptibility of 2195 aluminum-lithium alloy was investigated by means of split Hopkinson pressure bar. The stress collapse in true stress-true strain curves and true stress-time curves was observed. The adiabatic shear susceptibility of different aging statuses and strain rate were discussed by means of metallography observation. The critical strain, stress collapse time and formation energy of adiabatic shear bands were compared. The results show that different aging statuses and strain rate have significant influences on adiabatic shear behaviors of 2195 aluminum-lithium alloy. The peak-aged specimen has the highest adiabatic shearing susceptibility, while the under-aged specimen has the least adiabatic shear susceptibility. The susceptibility of adiabatic shearing increases with the increases of strain rate.

Large strain deformation behavior of polymeric gels in shear- and cavitation rheology

Science.gov (United States)

Hashemnejad, Seyed Meysam; Kundu, Santanu

Polymeric gels are used in many applications including in biomedical and in food industries. Investigation of mechanical responses of swollen polymer gels and linking that to the polymer chain dynamics are of significant interest. Here, large strain deformation behavior of two different gel systems and with different network architecture will be presented. We consider biologically relevant polysaccharide hydrogels, formed through ionic and covalent crosslinking, and physically associating triblock copolymer gels in a midblock selective solvent. Gels with similar low-strain shear modulus display distinctly different non-linear rheological behavior in large strain shear deformation. Both these gels display strain-stiffening behavior in shear-deformation prior to macroscopic fracture of the network, however, only the alginate gels display negative normal stress. The cavitation rheology data show that the critical pressure for cavitation is higher for alginate gels than that observed for triblock gels. These distinctly different large-strain deformation behavior has been related to the gel network structure, as alginate chains are much stiffer than the triblock polymer chains.

The Effects of Shear Strain, Fabric, and Porosity Evolution on Elastic and Mechanical Properties of Clay-Rich Fault Gouge

Science.gov (United States)

Kenigsberg, A.; Saffer, D. M.; Riviere, J.; Marone, C.

2017-12-01

Ultrasonic/seismic waves are widely used for probing fault zone elastic and mechanical properties (gouge composition, frictional strength, density) and elastic properties (Vp, Vs, bulk and shear moduli), as it can provide insight into key processes and fault properties during shearing. These include fabric and force chain formation, porosity evolution, and fault zone stiffness, which are in turn factors in fault slip, damage, and healing. We report on a suite of direct shear experiments on synthetic fault gouge composed of 50% smectite /50% quartz at a normal stress of 25 MPa, in which we use ultrasonic wave transmission to continuously monitor compressional and shear wave velocities (Vp, Vs) up to shear strains of 25, while simultaneously measuring friction and monitoring the evolution of density and porosity. We find that wavespeeds vary with shear strain, due to fabric development and the evolution of density and porosity. The coefficient of friction peaks at μ .47 at a shear strain of .5 - 1, decreases to a steady state value of μ .43 by shear strains of 4.5- 6 and then remains rather constant to shear strains of 6 - 25, consistent with previous work. Density increases rapidly from 1.78 g/cm3 to 1.83 g/cm3 at shear strains from 0-2 (porosity decreases from 33% to 25% over that range), and then more gradually increases to a density of 2.08 g/cm3 (porosity of 21%) at a shear strain of 25. Vp increases from 2400 m/s to 2900 m/s during the onset of shear until a shear strain of 3, and then decreases to 2400-2500 by shear strain of 7-9. At shear strains above 9, Vp slowly increases as the layer becomes denser and less porous. We interpret the co-evolving changes in friction, porosity, and elastic moduli/wavespeed to reflect fabric development and alignment of clay particles as a function of shearing. More specifically, the decrease in Vp at a shear strain of 3 reflects the clay particles gradually aligning. Once the particles are aligned, the gradual increase of

The Influence of Forming Directions and Strain Rate on Dynamic Shear Properties of Aerial Aluminum Alloy

Directory of Open Access Journals (Sweden)

Ying Meng

2018-03-01

Full Text Available Dynamic shear properties under high strain rate are an important basis for studying the dynamic mechanical properties and microscopic mechanisms of materials. Dynamic impact shear tests of aerial aluminum alloy 7050-T7451 in rolling direction (RD, transverse direction (TD and normal direction (ND were performed at a range of strain rates from 2.5 × 104 s−1 to 4.5 × 104 s−1 by High Split Hopkinson Pressure Bar (SHPB. The influence of different forming directions and strain rates on the dynamic shear properties of material and the microstructure evolution under dynamic shear were emphatically analyzed. The results showed that aluminum alloy 7050-T7451 had a certain strain rate sensitivity and positive strain rate strengthening effect, and also the material had no obvious strain strengthening effect. Different forming directions had a great influence on dynamic shear properties. The shear stress in ND was the largest, followed by that in RD, and the lowest was that in TD. The microstructure observation showed that the size and orientation of the grain structure were different in three directions, which led to the preferred orientation of the material. All of those were the main reasons for the difference of dynamic shear properties of the material.

Finite Strain Analysis of the Wadi Fatima Shear Zone in Western Arabia, Saudi Arabia

Science.gov (United States)

Kassem, O. M. K.; Hamimi, Z.

2018-03-01

Neoproterozoic rocks, Oligocene to Neogene sediments and Tertiary Red Sea rift-related volcanics (Harrat) are three dominant major groups exposed in the Jeddah tectonic terrane in Western Arabia. The basement complex comprises amphibolites, schists, and older and younger granites unconformably overlain by a post-amalgamation volcanosedimentary sequence (Fatima Group) exhibiting post-accretionary thrusting and thrust-related structures. The older granites and/or the amphibolites and schists display mylonitization and shearing in some outcrops, and the observed kinematic indicators indicate dextral monoclinic symmetry along the impressive Wadi Fatima Shear Zone. Finite strain analysis of the mylonitized lithologies is used to interpret the deformation history of the Wadi Fatima Shear Zone. The measured finite strain data demonstrate that the amphibolites, schists, and older granites are mildly to moderately deformed, where XZ (axial ratios in XZ direction) vary from 2.76 to 4.22 and from 2.04 to 3.90 for the Rf/φ and Fry method respectively. The shortening axes ( Z) have subvertical attitude and are associated with subhorizontal foliation. The data show oblate strain ellipsoids in the different rocks in the studied area and indication bulk flattening strain. We assume that the different rock types have similar deformation behavior. In the deformed granite, the strain data are identical in magnitude with those obtained in the Fatima Group volcanosedimentary sequence. Finite strain accumulated without any significant volume change contemporaneously with syn-accretionary transpressive structures. It is concluded that a simple-shear deformation with constant-volume plane strain exists, where displacement is strictly parallel to the shear plane. Furthermore, the contacts between various lithological units in the Wadi Fatima Shear Zone were formed under brittle to semi-ductile deformation conditions.

Strain-induced shear instability in Liverpool Bay

Science.gov (United States)

Wihsgott, Juliane; Palmer, Matthew R.

2013-04-01

Liverpool Bay is a shallow subsection of the eastern Irish Sea with large tides (10 m), which drive strong tidal currents (1 ms-1). The Bay is heavily influenced by large freshwater inputs from several Welsh and English rivers that maintain a strong and persistent horizontal density gradient. This gradient interacts with the sheared tidal currents to strain freshwater over denser pelagic water on a semi-diurnal frequency. This Strain-Induced-Periodic-Stratification (SIPS) has important implications on vertical and horizontal mixing. The subtle interaction between stratification and turbulence in this complex environment is shown to be of critical importance to freshwater transport, and subsequently the fate of associated biogeochemical and pollutant pathways. Recent work identified an asymmetry of current ellipses due to SIPS that increases shear instability in the halocline with the potential to enhance diapycnal mixing. Here, we use data from a short, high intensity process study which reveals this mid-water mechanism maintains prolonged periods of sub-critical gradient Richardson number (Ri ≤ ¼) that suggests shear instability is likely. A time series of measurements from a microstructure profiler identifies the associated increase in turbulence is short lived and 'patchy' but sufficient to promote diapycnal mixing. The significance of this mixing process is further investigated by comparing our findings with long-term observations from the Liverpool Bay Coastal Observatory. We identify that the conditions for shear instability during SIPS are regularly met and suggest that this process contributes to the current underestimates of near coastal mixing observed in regional models. To assist our understanding of the observed processes and to test the current capability of turbulence 'closure schemes' we employ a one-dimensional numerical model to investigate the physical mechanisms driving diapycnal mixing in Liverpool Bay.

Theory and Practice of Shear/Stress Strain Gage Hygrometry

Science.gov (United States)

Shams, Qamar A.; Fenner, Ralph L.

2006-01-01

Mechanical hygrometry has progressed during the last several decades from crude hygroscopes to state-of-the art strain-gage sensors. The strain-gage devices vary from different metallic beams to strain-gage sensors using cellulose crystallite elements, held in full shear restraint. This old technique is still in use but several companies are now actively pursuing development of MEMS miniaturized humidity sensors. These new sensors use polyimide thin film for water vapor adsorption and desorption. This paper will provide overview about modern humidity sensors.

A New Accurate yet Simple Shear Flexible Triangular Plate Element with Linear Bending Strains

DEFF Research Database (Denmark)

Damkilde, Lars; Pedersen, Ronnie

2010-01-01

The paper describes a new shear flexible triangular element. The formulation is based on displacement interpolation of the transverse displacement of the midsurface and the rotations of the cross-sections, and the element is fully compatible. The basic principle is to use a so-called balanced...... interpolation so that the part of the shear strains that relates to the transverse displacement has the same polynomial variation as the part of the shear strains that relates to the rotations of the cross-section. This balanced interpolation in combination with complete polynomial interpolations prevents shear...... are virtually the same. The slightly incompatible formulation can be implemented directly into commercial codes....

The role of strain localization in the fracture of irradiated pressure tube material

International Nuclear Information System (INIS)

Dutton, R.

1989-04-01

This report reviews those phenomena that lead to strain localization in zirconium alloys, with particular reference to the role played by the formation of shear bands in fracture processes. The important influence of plastic deformation, in general, on fracture mechanisms is emphasized. This is to be expected when elastic-plastic fracture mechanics is the chosen analytical technique. Intensely inhomogeneous characteristics of strain localization cause an abrupt bifurcation in the evolution of deformation strain and lead to plastic instability linked with intrinsic material behaviour (e.g., work softening) or of geometric origin (e.g., localized necking). Both of these effects are discussed in relation to measurable deformation parameters, such as the work hardening rate and strain rate sensitivity, which determine the degree of resistance to plastic instability. The modifying effect of irradiation on these quantities is given specific attention, the appropriate literature pertaining to Zircaloy and Zr-2.5% Nb being reviewed. Recommendations are made for a combined experimental and theoretical program to characterize strain localization and reduced ductility in irradiated cold-worked Zr-2.5% Nb pressure tube material. The relationship between the deformation properties and the fracture behaviour is discussed

The occurrence of shear banding in a millimeter scale (12-bar3)[634] grain of an Al-4.5% Mg alloy during plane strain compression

International Nuclear Information System (INIS)

Chapelle, David; Darrieulat, Michel

2003-01-01

The appearance of localization in shear bands during plane strain compression (PSC) of an Al-4.5% Mg alloy is investigated, with emphasis on a millimeter scale S-orientated grain in the longitudinal section of the specimen, upon which a gold microgrid was deposited. In order to justify this focus, attention is also paid on smaller grains of other areas. The microgrid technique allows the local strain field at various steps of deformation to be followed and in-plane components to be plotted over the selected region. Electron back scattered diffraction analysis was also used to gain an insight into the crystallography of local lattice rotations. One can then predict the potentially activated slip systems according to the Schmid law with Taylor's hypothesis, and assert the initial crystallographic feature of shear banding. This provides the opportunity to gain a more complete understanding, assuming a grain scale effect, of the mechanisms involved in the occurrence of shear banding in this alloy, and to reveal its influence on the rolling texture

Shear localization and effective wall friction in a wall bounded granular flow

Science.gov (United States)

Artoni, Riccardo; Richard, Patrick

2017-06-01

In this work, granular flow rheology is investigated by means of discrete numerical simulations of a torsional, cylindrical shear cell. Firstly, we focus on azimuthal velocity profiles and study the effect of (i) the confining pressure, (ii) the particle-wall friction coefficient, (iii) the rotating velocity of the bottom wall and (iv) the cell diameter. For small cell diameters, azimuthal velocity profiles are nearly auto-similar, i.e. they are almost linear with the radial coordinate. Different strain localization regimes are observed : shear can be localized at the bottom, at the top of the shear cell, or it can be even quite distributed. This behavior originates from the competition between dissipation at the sidewalls and dissipation in the bulk of the system. Then we study the effective friction at the cylindrical wall, and point out the strong link between wall friction, slip and fluctuations of forces and velocities. Even if the system is globally below the sliding threshold, force fluctuations trigger slip events, leading to a nonzero wall slip velocity and an effective wall friction coefficient different from the particle-wall one. A scaling law was found linking slip velocity, granular temperature in the main flow direction and effective friction. Our results suggest that fluctuations are an important ingredient for theories aiming to capture the interface rheology of granular materials.

Magnetic fabric of sheared till: A strain indicator for evaluating the bed deformation model of glacier flow

Science.gov (United States)

Hooyer, T.S.; Iverson, N.R.; Lagroix, F.; Thomason, J.F.

2008-01-01

Wet-based portions of ice sheets may move primarily by shearing their till beds, resting in high sediment fluxes and the development of subglacial landforms. This model of glacier movement, which requires high bed shear strains, can be tested using till microstructural characteristics that evolve during till deformation. Here we examine the development of magnetic fabric using a ring shear device to defom two Wisconsin-age basal tills to shear strains as high as 70. Hysteresis experiments and the dependence of magnetic susceptibility of these tills on temperature demonstrate that anisotropy of magnetic susceptibility (AMS) develops during shear due to the rotation of primarily magnetite particles that are silt sized or smaller. At moderate shear strains (???6-25), principal axes of maximum magnetic susceptibility develop a strong fabric (S1 eignevalues of 0.83-0.96), without further strengthening at higher strains, During deformation, directions of maximum susceptibility cluster strongly in the direction of shear and plunge 'up-glacier,' consistent with the behavior of pebbles and sand particles studied in earlier experiments. In contrast, the magnitude of AMS does not vary systematically with strain and is small relative to its variability among samples; this is because most magnetite grains are contained as inclusions in larger particles and hence do not align during shear. Although processes other than pervasive bed deformation may result in strong flow parallel fabrics, AMS fabrics provide a rapid and objective means of identifying basal tills that have not been sheared sufficiently to be compatible with the bed deformation model. Copyright 2008 by the American Geophysical Union.

Shear-coupled grain-boundary migration dependence on normal strain/stress

Science.gov (United States)

Combe, N.; Mompiou, F.; Legros, M.

2017-08-01

In specific conditions, grain-boundary (GB) migration occurs in polycrystalline materials as an alternative vector of plasticity compared to the usual dislocation activity. The shear-coupled GB migration, the expected most efficient GB based mechanism, couples the GB motion to an applied shear stress. Stresses on GB in polycrystalline materials seldom have, however, a unique pure shear component. This work investigates the influence of a normal strain on the shear coupled migration of a Σ 13 (320 )[001 ] GB in a copper bicrystal using atomistic simulations. We show that the yield shear stress inducing the GB migration strongly depends on the applied normal stress. Beyond, the application of a normal stress on this GB qualitatively modifies the GB migration: while the Σ 13 (320 )[001 ] GB shear couples following the 〈110 〉 migration mode without normal stress, we report the observation of the 〈010 〉 mode under a sufficiently high tensile normal stress. Using the nudge elastic band method, we uncover the atomistic mechanism of this 〈010 〉 migration mode and energetically characterize it.

Shear Strains, Strain Rates and Temperature Changes in Adiabatic Shear Bands

Science.gov (United States)

1980-05-01

X14A. It has been found that when bainitic and martensitic steels are sheared adiabatically, a layer of material within ths shear zone is altezed and...Sooiety for Metals, Metals Park, Ohio, 1978, pp. 148-0. 21 TABLE II SOLID-STATE TRANSFORMATIONS IN BAINITIC STEEL TRANSFORMATION TRANSFORMATION...shear, thermoplastic, plasticity, plastic deformation, armor, steel IL AnSRACT ( -=nba asoa.tm a naeoesM iN faity by bleak n bet/2972 Experiments

High-Strain Rate Failure Modeling Incorporating Shear Banding and Fracture

Science.gov (United States)

2017-11-22

High Strain Rate Failure Modeling Incorporating Shear Banding and Fracture The views, opinions and/or findings contained in this report are those of...SECURITY CLASSIFICATION OF: 1. REPORT DATE (DD-MM-YYYY) 4. TITLE AND SUBTITLE 13. SUPPLEMENTARY NOTES 12. DISTRIBUTION AVAILIBILITY STATEMENT 6. AUTHORS...Report as of 05-Dec-2017 Agreement Number: W911NF-13-1-0238 Organization: Columbia University Title: High Strain Rate Failure Modeling Incorporating

Atomic mechanism of shear localization during indentation of a nanostructured metal

International Nuclear Information System (INIS)

Sansoz, F.; Dupont, V.

2007-01-01

Shear localization is an important mode of deformation in nanocrystalline metals. However, it is very difficult to verify the existence of local shear planes in nanocrystalline metals experimentally. Sharp indentation techniques may provide novel opportunities to investigate the effect of shear localization at different length scales, but the relationship between indentation response and atomic-level shear band formation has not been fully addressed. This paper describes an effort to provide direct insight on the mechanism of shear localization during indentation of nanocrystalline metals from atomistic simulations. Molecular statics is performed with the quasi-continuum method to simulate the indentation of single crystal and nanocrystalline Al with a sharp cylindrical probe. In the nanocrystalline regime, two grain sizes are investigated, 5 nm and 10 nm. We find that the indentation of nanocrystalline metals is characterized by serrated plastic flow. This effect seems to be independent of the grain size. Serration in nanocrystalline metals is found to be associated with the formation of shear bands by sliding of aligned interfaces and intragranular slip, which results in deformation twinning

Large strain variable stiffness composites for shear deformations with applications to morphing aircraft skins

Science.gov (United States)

McKnight, G. P.; Henry, C. P.

2008-03-01

Morphing or reconfigurable structures potentially allow for previously unattainable vehicle performance by permitting several optimized structures to be achieved using a single platform. The key to enabling this technology in applications such as aircraft wings, nozzles, and control surfaces, are new engineered materials which can achieve the necessary deformations but limit losses in parasitic actuation mass and structural efficiency (stiffness/weight). These materials should exhibit precise control of deformation properties and provide high stiffness when exercised through large deformations. In this work, we build upon previous efforts in segmented reinforcement variable stiffness composites employing shape memory polymers to create prototype hybrid composite materials that combine the benefits of cellular materials with those of discontinuous reinforcement composites. These composites help overcome two key challenges for shearing wing skins: the resistance to out of plane buckling from actuation induced shear deformation, and resistance to membrane deflections resulting from distributed aerodynamic pressure loading. We designed, fabricated, and tested composite materials intended for shear deformation and address out of plane deflections in variable area wing skins. Our designs are based on the kinematic engineering of reinforcement platelets such that desired microstructural kinematics is achieved through prescribed boundary conditions. We achieve this kinematic control by etching sheets of metallic reinforcement into regular patterns of platelets and connecting ligaments. This kinematic engineering allows optimization of materials properties for a known deformation pathway. We use mechanical analysis and full field photogrammetry to relate local scale kinematics and strains to global deformations for both axial tension loading and shear loading with a pinned-diamond type fixture. The Poisson ratio of the kinematically engineered composite is ~3x higher than

Periodic Viscous Shear Heating Instability in Fine-Grained Shear Zones: Possible Mechanism for Intermediate Depth Earthquakes and Slow Earthquakes?

Science.gov (United States)

Kelemen, P. B.; Hirth, G.

2004-12-01

Localized ductile shear zones with widths of cm to m are observed in exposures of Earth's shallow mantle (e.g., Kelemen & Dick JGR 95; Vissers et al. Tectonophys 95) and dredged from oceanic fracture zones (e.g., Jaroslow et al. Tectonophys 96). These are mylonitic (grain size 10 to 100 microns) and record mineral cooling temperatures from 1100 to 600 C. Pseudotachylites in a mantle shear zone show that shear heating temperatures can exceed the mantle solidus (e.g., Obata & Karato Tectonophys 95). Simple shear, recrystallization, and grain boundary sliding all decrease the spacing between pyroxenes, so olivine grain growth at lower stress is inhibited; thus, once formed, these shear zones do not "heal" on geological time scales. Reasoning that grain-size sensitive creep will be localized within these shear zones, rather than host rocks (grain size 1 to 10 mm), and inspired by the work of Whitehead & Gans (GJRAS 74), we thought these might undergo repeated shear heating instabilities. In this view, as elastic stress increases, the shear zone weakens via shear heating; rapid deformation of the weak shear zone releases most stored elastic stress; lower stress and strain rate coupled with diffusion of heat into host rocks leads to cooling and strengthening, after which the cycle repeats. We constructed a simple numerical model incorporating olivine flow laws for dislocation creep, diffusion creep, grain boundary sliding, and low T plasticity. We assumed that viscous deformation remains localized in shear zones, surrounded by host rocks undergoing elastic deformation. We fixed the velocity along one side of an elastic half space, and calculated stress due to elastic strain. This stress drives viscous deformation in a shear zone of specified width. Shear heating and thermal diffusion control temperature evolution in the shear zone and host rocks. A maximum of 1400 C (where substantial melting of peridotite would occur) is imposed. Grain size evolves during dislocation

Effect of shear strain on the deflection of a clamped magnetostrictive film-substrate system

International Nuclear Information System (INIS)

Ming Zhenghui; Ming Li; Bo Zou; Xia Luo

2011-01-01

The effect of in-plane shear strain of a clamped bimorph on the deflection produced by magnetization of the film is investigated. The deflection is found by minimizing the Gibbs free energy with respect to four parameters, strains and curvatures along x and y directions at the interface, by assuming that the curvature in the y direction varies as a function of aspect ratio w/l along x. A set of standard linear equations of four parameters are obtained and the deflection is expressed in terms of the four parameters by solving the equations using Cramer rules. The inconsistencies pointed out by previous authors are also reviewed. For actuators made of thick and short clamped film-substrate system, the in-plane shear deformation should not be omitted. The present calculation model can give a relatively simple and accurate prediction of deflection for thick and short specimens of aspect ratio w/l<10, which supports the results obtained by finite element modeling. - Highlights: → We model the deflection of a thick magnetostrictive film-substrate cantilever plate. → Total stress along z from magnetic field is not zero without external force. → Effect of in-plane shear strain in calculating deflection examined. → Analytical solution of deflection obtained by assuming a curvature function. → Shear strain for short cantilever film-substrate plate considered.

Orientations and Relative Shear-strain Response Coefficients for PBO Gladwin Tensor Strainmeters from Teleseismic Love Waves

Science.gov (United States)

Roeloffs, E. A.

2016-12-01

A Gladwin Tensor Strainmeter (GTSM) is designed to measure changes of the horizontal strain tensor, derived as linear combinations of radial elongations or contractions of the strainmeter's cylindrical housing measured at four azimuths. Each radial measurement responds to changes in the areal, horizontal shear and vertical components of the strain tensor in the surrounding formation. The elastic response coefficients to these components depend on the relative elastic moduli of the housing, formation, and cement. These coefficients must be inferred for each strainmeter after it is cemented into its borehole by analyzing the instrument response to well-characterized strain signals such as earth tides. For some GTSMs of the Earthscope Plate Boundary Observatory (PBO), however, reconciling observed earth-tide signals with modeled tidal strains requires response coefficients that differ substantially between the instrument's four gauges, and/or orientation corrections of tens of degrees. GTSM response coefficients can also be estimated from high-resolution records of teleseismic Love waves from great earthquakes around the world. Such records can be used in conjunction with apparent propagation azimuths from nearby broadband seismic stations to determine the GTSM's orientation. Knowing the orientation allows the ratios between the shear strain response coefficients of a GTSM's four gauges to be estimated. Applying this analysis to 14 PBO GTSMs confirms that orientations of some instruments differ significantly from orientations measured during installation. Orientations inferred from earth-tide response tend to agree with those inferred from Love waves for GTSMs far from tidal water bodies, but to differ for GTSMs closer to coastlines. Orientations derived from teleseismic Love waves agree with those estimated by Grant and Langston (2010) using strains from a broadband seismic array near Anza, California. PBO GTSM recordings of teleseismic Love waves show differences of

Strain mapping near a triple junction in strained Ni-based alloy using EBSD and biaxial nanogauges

Energy Technology Data Exchange (ETDEWEB)

Clair, A. [Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 5209 CNRS, Universite de Bourgogne, 9 Avenue Alain Savary, BP 47870, 21078 Dijon Cedex (France); Foucault, M.; Calonne, O. [Areva ANP, Centre Technique Departement Corrosion-Chimie, 30 Bd de l' industrie, BP 181, 71205 Le Creusot (France); Lacroute, Y.; Markey, L.; Salazar, M.; Vignal, V. [Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 5209 CNRS, Universite de Bourgogne, 9 Avenue Alain Savary, BP 47870, 21078 Dijon Cedex (France); Finot, E., E-mail: Eric.Finot@u-bourgogne.fr [Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 5209 CNRS, Universite de Bourgogne, 9 Avenue Alain Savary, BP 47870, 21078 Dijon Cedex (France)

2011-05-15

Research highlights: > Surface strains measured using nanogauge were compared to the texture obtained by EBSD. > Statistics of the principal strain discern the grains according to the Schmid factor. > Strain hotspots were localized near a triple junction of alloy 600 under tensile loading. > Asymetrical profile of the GB strains is a criterion for surface cracking initiation. - Abstract: A key element for analyzing the crack initiation in strained polycrystalline alloys is the local quantification of the surface strain distribution according to the grain texture. Using electron backscattered diffraction, the local microstructure was determined to both localize a triple junction and deduce the local Schmid factors. Kernel average misorientation (KAM) was also used to map the areas of defect concentration. The maximum principal strain and the in-plane shear strain were quantified using the biaxial nanogauge. Distortions of the array of nanodots used as spot markers were analyzed near the triple junction. The crystallographic orientation and the surface strain were then investigated both statistically for each grain and locally at the grain boundaries. The superimposition of microstructure and strain maps allows the high strain gradient (reaching 3-fold the applied strain) to be localized at preferential grain boundaries near the triple junction. The Schmid factors and the KAM were compared to the maximum principal strain and the in-plane shear strain respectively. The polycrystalline deformation was attributable first to the rotation of some grains, followed by the elongation of all grains along their preferential activated slip systems.

Micromechanical analysis of martensite distribution on strain localization in dual phase steels by scanning electron microscopy and crystal plasticity simulation

Energy Technology Data Exchange (ETDEWEB)

Jafari, M. [Department of Mechanical Engineering, Isfahan University of Technology, Isfahan (Iran, Islamic Republic of); Ziaei-Rad, S., E-mail: szrad@cc.iut.ac.ir [Department of Mechanical Engineering, Isfahan University of Technology, Isfahan (Iran, Islamic Republic of); Saeidi, N. [Department of Materials Engineering, Isfahan University of Technology, Isfahan (Iran, Islamic Republic of); Jamshidian, M. [Department of Mechanical Engineering, Isfahan University of Technology, Isfahan (Iran, Islamic Republic of)

2016-07-18

The morphology and distribution of the dispersed martensite islands in the ferrite matrix plays a key role in the formation of shear bands in dual phase steels. In this study, we investigate the relationship between the martensite dispersion and the strain localization regions due to the formation of shear bands in fine-grained DP 780 steel, employing experimental observations as well as numerical simulations. SEM studies of the deformed microstructure showed that voids nucleated at ferrite-martensite interface within larger ferrite grains and regions with low local martensite fraction. The experimental results were precisely analyzed by finite element simulations based on the theory of crystal plasticity. A parametric study was then performed to obtain a deeper insight in to the effect of martensite dispersion on the strain localization of the neighboring ferrite. Crystal plasticity simulation results revealed that in a more regular structure compared to a random structure, a greater region of the ferrite phase contributes to accommodate plasticity. In addition, these regions limit the formation of main shear bands by creating barriers against stress concentration regions, results in lower growth and interaction of stress concentration regions with each others.

Discrete Analysis of Damage and Shear Banding in Argillaceous Rocks

Science.gov (United States)

Dinç, Özge; Scholtès, Luc

2018-05-01

A discrete approach is proposed to study damage and failure processes taking place in argillaceous rocks which present a transversely isotropic behavior. More precisely, a dedicated discrete element method is utilized to provide a micromechanical description of the mechanisms involved. The purpose of the study is twofold: (1) presenting a three-dimensional discrete element model able to simulate the anisotropic macro-mechanical behavior of the Callovo-Oxfordian claystone as a particular case of argillaceous rocks; (2) studying how progressive failure develops in such material. Material anisotropy is explicitly taken into account in the numerical model through the introduction of weakness planes distributed at the interparticle scale following predefined orientation and intensity. Simulations of compression tests under plane-strain and triaxial conditions are performed to clarify the development of damage and the appearance of shear bands through micromechanical analyses. The overall mechanical behavior and shear banding patterns predicted by the numerical model are in good agreement with respect to experimental observations. Both tensile and shear microcracks emerging from the modeling also present characteristics compatible with microstructural observations. The numerical results confirm that the global failure of argillaceous rocks is well correlated with the mechanisms taking place at the local scale. Specifically, strain localization is shown to directly result from shear microcracking developing with a preferential orientation distribution related to the orientation of the shear band. In addition, localization events presenting characteristics similar to shear bands are observed from the early stages of the loading and might thus be considered as precursors of strain localization.

Comparison and Combination of Strain and Shear Wave Elastography of Breast Masses for Differentiation of Benign and Malignant Lesions by Quantitative Assessment: Preliminary Study.

Science.gov (United States)

Seo, Mirinae; Ahn, Hye Shin; Park, Sung Hee; Lee, Jong Beum; Choi, Byung Ihn; Sohn, Yu-Mee; Shin, So Youn

2018-01-01

To compare the diagnostic performance of strain and shear wave elastography of breast masses for quantitative assessment in differentiating benign and malignant lesions and to evaluate the diagnostic accuracy of combined strain and shear wave elastography. Between January and February 2016, 37 women with 45 breast masses underwent both strain and shear wave ultrasound (US) elastographic examinations. The American College of Radiology Breast Imaging Reporting and Data System (BI-RADS) final assessment on B-mode US imaging was assessed. We calculated strain ratios for strain elastography and the mean elasticity value and elasticity ratio of the lesion to fat for shear wave elastography. Diagnostic performances were compared by using the area under the receiver operating characteristic curve (AUC). The 37 women had a mean age of 47.4 years (range, 20-79 years). Of the 45 lesions, 20 were malignant, and 25 were benign. The AUCs for elasticity values on strain and shear wave elastography showed no significant differences (strain ratio, 0.929; mean elasticity, 0.898; and elasticity ratio, 0.868; P > .05). After selectively downgrading BI-RADS category 4a lesions based on strain and shear wave elastographic cutoffs, the AUCs for the combined sets of B-mode US and elastography were improved (B-mode + strain, 0.940; B-mode + shear wave; 0.964; and B-mode, 0.724; P shear wave elastography showed significantly higher diagnostic accuracy than each individual elastographic modality (P = .031). These preliminary results showed that strain and shear wave elastography had similar diagnostic performance. The addition of strain and shear wave elastography to B-mode US improved diagnostic performance. The combination of strain and shear wave elastography results in a higher diagnostic yield than each individual elastographic modality. © 2017 by the American Institute of Ultrasound in Medicine.

Development of Generalized Correlation Equation for the Local Wall Shear Stress

International Nuclear Information System (INIS)

Jeon, Yu Mi; Park, Ju Hwan

2010-06-01

The pressure drop characteristics for a fuel channel are essential for the design and reliable operation of a nuclear reactor. Over several decades, analytical methods have been developed to predict the friction factor in the fuel bundle flows. In order to enhance the accuracy of prediction for the pressure drop in a rod bundle, the influences of a channel wall and the local shear stress distribution should be considered. Therefore, the correlation equation for a local wall shear stress distribution should be developed in order to secure an analytical solution for the friction factor of a rod bundle. For a side subchannel, which has the influence of the channel wall, the local wall shear stress distribution is dependent on the ratio of wall to diameter (W/D) as well as the ratio of pitch to diameter (P/D). In the case that W/D has the same value with P/D, the local shear stress distribution can be simply correlated with the function of angular position for each value of P/D. While in the case where W/D has a different value than P/D, the correlation equation should be developed for each case of P/D and W/D. Therefore, in the present study, the generalized correlation equation of the local wall shear stress distribution was developed for a side subchannel in the case where W/D has a different value than P/D. Consequently, the generalized correlation equation of a local wall shear stress distribution can be represented by the equivalent pitch to diameter ratio, P'/D for the case that P/D and W/D had a different value

Strain localization in the lower crust: brittle precursors versus lithological heterogeneities (Musgrave Ranges, Central Australia)

Science.gov (United States)

Hawemann, Friedrich; Mancktelow, Neil; Wex, Sebastian; Pennacchioni, Giorgio; Camacho, Alfredo

2016-04-01

The Davenport shear zone in Central Australia is a strike-slip ductile shear zone developed during the Petermann Orogeny (~ 550 Ma). The conditions of shearing are estimated to be amphibolite-eclogite facies (650 °C, 1.2 GPa). The up to seven kilometre thick mylonite zone encloses several large low strain domains with excellent exposure, thus allowing a thorough study of the initiation of shear zones. Quartzo-feldspathic gneisses and granitoids inherit a suite of lithological heterogeneities such as quartz-rich pegmatites, mafic layers and dykes. When in a favourable orientation to the shortening direction, these rheologically different pre-existing layers might be expected to localize deformation. However, with the singular exception of long, continuous and fine-grained dolerite dykes, this is not observed. Quartz-rich pegmatites are mostly unsheared, even if in a favourable orientation, and sometimes boudinaged or folded. There are instead many shear zones only a few mm to cm in width, extending up to tens of metres, which are in fact oriented at a very high angle to the shortening direction. Parallel to these, a network of little to moderately overprinted brittle fractures are observed, commonly marked by pseudotachylyte (pst) and sometimes new biotite. Shear reactivation of these precursor fractures is generally limited to the length of the initial fracture and typically re-uses and shears the pst. The recrystallized mineral assemblage in the sheared pst consists of Cpx+Grt+Fsp±Ky and is the same to that in the adjacent sheared gneiss, with the same PT estimates (650 °C, 1.2 GPa). In some cases, multiple generations of cross-cutting and sheared pst demonstrate alternating fracture and flow during progressive shear zone development and a clear tendency for subsequent pst formation to also localize in the existing shear zone. The latest pst may be both unsheared and unrecrystallized (no grt) and is probably related to a late stage, still localized within the

Comparison of strain and shear wave elastography for qualitative and quantitative assessment of breast masses in the same population.

Science.gov (United States)

Kim, Hyo Jin; Kim, Sun Mi; Kim, Bohyoung; La Yun, Bo; Jang, Mijung; Ko, Yousun; Lee, Soo Hyun; Jeong, Heeyeong; Chang, Jung Min; Cho, Nariya

2018-04-18

We investigated addition of strain and shear wave elastography to conventional ultrasonography for the qualitative and quantitative assessment of breast masses; cut-off points were determined for strain ratio, elasticity ratio, and visual score for differentiating between benign and malignant masses. In all, 108 masses from 94 patients were evaluated with strain and shear wave elastography and scored for suspicion of malignancy, visual score, strain ratio, and elasticity ratio. The diagnostic performance between ultrasonography alone and ultrasonography combined with either type of elastography was compared; cut-off points were determined for strain ratio, elasticity ratio, and visual score. Of the 108 masses, 44 were malignant and 64 were benign. The areas under the curves were significantly higher for strain and shear wave elastography-supplemented ultrasonography (0.839 and 0.826, respectively; P = 0.656) than for ultrasonography alone (0.764; P = 0.018 and 0.035, respectively). The diagnostic performances of strain and elasticity ratios were similar when differentiating benign from malignant masses. Cut-off values for strain ratio, elasticity ratio, and visual scores for strain and shear wave elastography were 2.93, 4, 3, and 2, respectively. Both forms of elastography similarly improved the diagnostic performance of conventional ultrasonography in the qualitative and quantitative assessment of breast masses.

Mechanical properties and local mobility of atactic-polystyrene films under constant-shear deformation

NARCIS (Netherlands)

Hudzinskyy, D.; Michels, M.A.J.; Lyulin, A.V.

2012-01-01

We have performed molecular-dynamics simulations of atactic polystyrene thin films to study the effect of shear rate, pressure, and temperature on the stress-strain behaviour, the relevant energetic contributions and non-affine displacements of polymer chains during constant-shear deformation. Under

Effect of Different Loading Conditions on the Nucleation and Development of Shear Zones Around Material Heterogeneities

Science.gov (United States)

Rybacki, E.; Nardini, L.; Morales, L. F.; Dresen, G.

2017-12-01

Rock deformation at depths in the Earth's crust is often localized in high temperature shear zones, which occur in the field at different scales and in a variety of lithologies. The presence of material heterogeneities has long been recognized to be an important cause for shear zones evolution, but the mechanisms controlling initiation and development of localization are not fully understood, and the question of which loading conditions (constant stress or constant deformation rate) are most favourable is still open. To better understand the effect of boundary conditions on shear zone nucleation around heterogeneities, we performed a series of torsion experiments under constant twist rate (CTR) and constant torque (CT) conditions in a Paterson-type deformation apparatus. The sample assemblage consisted of copper-jacketed Carrara marble hollow cylinders with one weak inclusion of Solnhofen limestone. The CTR experiments were performed at maximum bulk strain rates of 1.8-1.9*10-4 s-1, yielding shear stresses of 19-20 MPa. CT tests were conducted at shear stresses between 18.4 and 19.8 MPa resulting in shear strain rates of 1-2*10-4 s-1. All experiments were run at 900 °C temperature and 400 MPa confining pressure. Maximum bulk shear strains (γ) were ca. 0.3 and 1. Strain localized within the host marble in front of the inclusion in an area termed process zone. Here grain size reduction is intense and local shear strain (estimated from markers on the jackets) is up to 8 times higher than the applied bulk strain, rapidly dropping to 2 times higher at larger distance from the inclusion. The evolution of key microstructural parameters such as average grain size and average grain orientation spread (GOS, a measure of lattice distortion) within the process zone, determined by electron backscatter diffraction analysis, differs significantly as a function of loading conditions. Both parameters indicate that, independent of bulk strain and distance from the inclusion, the

Adiabatic shear bands as predictors of strain rate in high speed machining of ramax-2

International Nuclear Information System (INIS)

Zeb, M.A.; Irfan, M.A.; Velduis, A.C.

2008-01-01

Shear band formation was studied in the chips obtained by turning of stainless steel- Ramax-2 (AISI 420F). The machining was performed on a CNC lathe using a PVD (Physical Vapor Deposition) cutting tool insert. The cutting speeds ranged from 50 m/ min to 250 m/min. Dry cutting conditions were employed. At cutting speeds higher than 30 m/mill, the chip did not remain intact with the workpiece using quick stop device. It was difficult to get the chip root SEM (Scanning Electron Microscope) micrographs at further higher speeds. Therefore, the width of the shear bands was used as the predictor of the strain rates involved at various cutting speeds. The results showed that the strain rates are quite in agreement with the amount of strain rate found during machining of such types of stainless steels. It was also observed that shear band density increased with increasing cutting speed. (author)

Rock mechanics observations pertinent to the rheology of the continental lithosphere and the localization of strain along shear zones

Science.gov (United States)

Kirby, S.H.

1985-01-01

the general phenomenon of ductile faulting in which ductile strains are localized into shear zones. Ductile faults have been produced in experiments of five different rock types and is generally expressed as strain softening in constant-strain-rate tests or as an accelerating-creep-rate stage at constant differential stress. A number of physical mechanisms have been identified that may be responsible for ductile faulting, including the onset of dynamic recrystallization, phase changes, hydrothermal alteration and hydrolytic weakening. Microscopic evidence for these processes as well as larger-scale geological and geophysical observations suggest that ductile faulting in the middle to lower crust and upper mantle may greatly influence the distribution and magnitudes of differential stresses and the style of deformation in the overlying upper continental lithosphere. ?? 1985.

Development of generalized correlation equation for the local wall shear stress

International Nuclear Information System (INIS)

Jeon, Yu Mi; Bae, Jun Ho; Park, Joo Hwan

2010-01-01

The pressure drop characteristics for a fuel channel are essential for the design and reliable operation of a nuclear reactor. Over several decades, analytical methods have been developed to predict the friction factor in the fuel bundle flows. In order to enhance the accuracy of prediction for the pressure drop in a rod bundle, the influences of a channel wall and the local shear stress distribution should be considered. Hence, the correlation equation for a local shear stress distribution should be developed in order to secure an analytical solution for the friction factor of a rod bundle. For a side subchannel, which has the influence of the channel wall, the local shear stress distribution is dependent on the ratio of wall to diameter (W/D) as well as the ratio of pitch to diameter (P/D). In the case that W/D has the same value with P/D, the local shear stress distribution can be simply correlated with the function of angular position for each value of P/D. While, in the case that W/D has the different value with P/D, the correlation equation should be developed for each case of P/D and W/D. Hence, in the present study, the generalized correlation equation of a local shear stress distribution is developed for a side subchannel in the case that W/D has the different value with P/D

Modeling of Mesoscale Variability in Biofilm Shear Behavior.

Directory of Open Access Journals (Sweden)

Pallab Barai

Full Text Available Formation of bacterial colonies as biofilm on the surface/interface of various objects has the potential to impact not only human health and disease but also energy and environmental considerations. Biofilms can be regarded as soft materials, and comprehension of their shear response to external forces is a key element to the fundamental understanding. A mesoscale model has been presented in this article based on digitization of a biofilm microstructure. Its response under externally applied shear load is analyzed. Strain stiffening type behavior is readily observed under high strain loads due to the unfolding of chains within soft polymeric substrate. Sustained shear loading of the biofilm network results in strain localization along the diagonal direction. Rupture of the soft polymeric matrix can potentially reduce the intercellular interaction between the bacterial cells. Evolution of stiffness within the biofilm network under shear reveals two regimes: a initial increase in stiffness due to strain stiffening of polymer matrix, and b eventual reduction in stiffness because of tear in polymeric substrate.

High-mode-number ballooning modes in a heliotron/torsatron system: 1, Local magnetic shear

International Nuclear Information System (INIS)

Nakajima, N.

1996-05-01

The characteristics of the local magnetic shear, a quantity associated with high-mode-number ballooning mode stability, are considered in heliotron/torsatron devices that have a large Shafranov shift. The local magnetic shear is shown to vanish even in the stellarator-like region in which the global magnetic shear is positive. The reason for this is that the degree of the local compression of the poloidal magnetic field on the outer side of the torus, which maintains the toroidal force balance, is reduced in the stellarator-like region of global magnetic shear because the global rotational transform in heliotron/torsatron systems is a radially increasing function. This vanishing of the local magnetic shear is a universal property in heliotron/torsatron systems with a large Shafranov shift since it results from toroidal force balance in the stellarator-like global shear regime that is inherent to such systems

Shear localization in a mature mylonitic rock analog during fast slip

Science.gov (United States)

Takahashi, M.; van den Ende, M. P. A.; Niemeijer, A. R.; Spiers, C. J.

2017-02-01

Highly localized slip zones developed within ductile shear zones, such as pseudotachylyte bands occurring within mylonitic fabric rocks, are frequently interpreted as evidence for earthquake nucleation and/or propagation within the ductile regime. To understand brittle/frictional shear localization processes in ductile shear zones and to relate these to earthquake nucleation and propagation, we performed tests with large changes in velocity on a brine-saturated, 80:20 (wt %) mixture of halite and muscovite gouge after forming a mature mylonitic structure through frictional-viscous flow. The direct effect a on shear strength that occurs in response to an instantaneous upward velocity-step is an important parameter in determining the nature of seismic rupture nucleation and propagation. We obtained reproducible results regarding low-velocity mechanical behavior compared with previous work, but also obtained new insights into effects of sudden increases in slip velocity on localization and strength evolution, at velocities above a critical velocity Vc (˜20 μm/s). We found that once a ductile, mylonitic structure has developed in a shear zone, subsequent cataclastic deformation is consistently localized in a narrow zone. This switch to localized deformation is controlled by the imposed velocity and becomes most apparent at velocities above Vc. In addition, the direct effect drops rapidly when the velocity exceeds Vc. This implies that slip can accelerate toward seismic velocities almost instantly and without much loss of fracture energy, once Vc is exceeded. Obtaining a measure for Vc in natural faults is therefore of key importance for understanding earthquake nucleation and propagation in the brittle-ductile transitional regime.

Domino structures evolution in strike-slip shear zones; the importance of the cataclastic flow

Science.gov (United States)

Moreira, N.; Dias, R.

2018-05-01

The Porto-Tomar-Ferreira do Alentejo dextral Shear Zone is one of the most important structures of the Iberian Variscides. In its vicinity, close to Abrantes (Central Portugal), a localized heterogeneous strain pattern developed in a decimetric metamorphic siliceous multilayer. This complex pattern was induced by the D2 dextral shearing of the early S0//S1 foliation in brittle-ductile conditions, giving rise to three main shear zone families. One of these families, with antithetic kinematics, delimits blocks with rigid clockwise rotation surrounded by coeval cataclasites, generating a local domino structure. The proposed geometrical and kinematic analysis, coupled with statistical studies, highlights the relation between subsidiary shear zones and the main shear zone. Despite the heterogeneous strain pattern, a quantitative approach of finite strain was applied based on the restoration of the initial fracture pattern. This approach shows the importance of the cataclastic flow coupled with the translational displacement of the domino domain in solving space problems related to the rigid block rotation. Such processes are key in allowing the rigid block rotation inside shear zones whenever the simple shear component is a fundamental mechanism.

Normal and Fibrotic Rat Livers Demonstrate Shear Strain Softening and Compression Stiffening: A Model for Soft Tissue Mechanics.

Directory of Open Access Journals (Sweden)

Maryna Perepelyuk

Full Text Available Tissues including liver stiffen and acquire more extracellular matrix with fibrosis. The relationship between matrix content and stiffness, however, is non-linear, and stiffness is only one component of tissue mechanics. The mechanical response of tissues such as liver to physiological stresses is not well described, and models of tissue mechanics are limited. To better understand the mechanics of the normal and fibrotic rat liver, we carried out a series of studies using parallel plate rheometry, measuring the response to compressive, extensional, and shear strains. We found that the shear storage and loss moduli G' and G" and the apparent Young's moduli measured by uniaxial strain orthogonal to the shear direction increased markedly with both progressive fibrosis and increasing compression, that livers shear strain softened, and that significant increases in shear modulus with compressional stress occurred within a range consistent with increased sinusoidal pressures in liver disease. Proteoglycan content and integrin-matrix interactions were significant determinants of liver mechanics, particularly in compression. We propose a new non-linear constitutive model of the liver. A key feature of this model is that, while it assumes overall liver incompressibility, it takes into account water flow and solid phase compressibility. In sum, we report a detailed study of non-linear liver mechanics under physiological strains in the normal state, early fibrosis, and late fibrosis. We propose a constitutive model that captures compression stiffening, tension softening, and shear softening, and can be understood in terms of the cellular and matrix components of the liver.

Structural mechanisms of formation of adiabatic shear bands

Directory of Open Access Journals (Sweden)

Mikhail Sokovikov

2016-10-01

Full Text Available The paper focuses on the experimental and theoretical study of plastic deformation instability and localization in materials subjected to dynamic loading and high-velocity perforation. We investigate the behavior of samples dynamically loaded during Hopkinson-Kolsky pressure bar tests in a regime close to simple shear conditions. Experiments were carried out using samples of a special shape and appropriate test rigging, which allowed us to realize a plane strain state. Also, the shear-compression specimens proposed in were investigated. The lateral surface of the samples was investigated in a real-time mode with the aid of a high-speed infra-red camera CEDIP Silver 450M. The temperature field distribution obtained at different time made it possible to trace the evolution of plastic strain localization. Use of a transmission electron microscope for studying the surface of samples showed that in the regions of strain localization there are parts taking the shape of bands and honeycomb structure in the deformed layer. The process of target perforation involving plug formation and ejection was investigated using a high-speed infra-red camera. A specially designed ballistic set-up for studying perforation was used to test samples in different impulse loading regimes followed by plastic flow instability and plug ejection. Changes in the velocity of the rear surface at different time of plug ejection were analyzed by Doppler interferometry techniques. The microstructure of tested samples was analyzed using an optical interferometer-profilometer and a scanning electron microscope. The subsequent processing of 3D deformation relief data enabled estimation of the distribution of plastic strain gradients at different time of plug formation and ejection. It has been found that in strain localization areas the subgrains are elongated taking the shape of bands and undergo fragmentation leading to the formation of super-microcrystalline structure, in which the

Local and Modal Damage Indicators for Reinforced Concrete Shear Frames Subject to Earthquakes

DEFF Research Database (Denmark)

Köylüoglu, H. U.; Nielsen, Søren R. K.; Abbott, J.

Local, modal and overall damage indicators for reinforced concrete shear frames subject to seismic excitation are defined and studied. Each storey of the shear frame is represented by a Clough and Johnston hysteretic oscillator with degrading elastic fraction of the restoring force. The local max...

Shear banding in large strain plasticity - Influence of specimen dimensions

Science.gov (United States)

Mucha, Marzena; Wcisło, Balbina; Pamin, Jerzy

2018-01-01

The paper deals with numerical analysis of shear banding which occurs in an elongated rectangular plate for a large strain elastic-plastic material model. It is focused on the influence of plate size proportions and finite element mesh density on numerical results. The discussion is limited to isothermal conditions and ideal plasticity. First a plain strain case is computed for different lengths of the plate, then simulations are repeated for plane stress for which different thicknesses of the plate are considered. Most of the computations are performed for three finite element meshes to verify discretization sensitivity of the results. The simulations are performed using AceGen and AceFEM packages for Wolfram Mathematica.

Local and global deformations in a strain-stiffening fibrin gel

Energy Technology Data Exchange (ETDEWEB)

Wen Qi [Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104 (United States); Basu, Anindita [Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104 (United States); Winer, Jessamine P [Institute for Medicine and Engineering, University of Pennsylvania, Philadelphia, PA 19104 (United States); Yodh, Arjun [Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104 (United States); Janmey, Paul A [Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104 (United States)

2007-11-15

Extracellular matrices composed of filamentous biopolymers like collagen and fibrin have viscoelastic properties that differ from those of rubberlike elastomers or hydrogels formed by flexible polymers. Compared to flexible polymer gels, filamentous biopolymer networks generally have larger elastic moduli, a striking increase in elastic modulus with increasing strain, and a pronounced negative normal stress when deformed in simple shear. All three of these unusual features can be accounted for by a theory that extends concepts of entropic elasticity to a regime where the polymer chains are already significantly extended in the absence of external forces because of their finite bending stiffness. An essential assumption of the theories that relate microscopic structural parameters such as persistence length and mesh size of biopolymer gels to their macroscopic rheology is that the deformation of these materials is affine: that is, the macroscopic strain of the bulk material is equal to the local strain within the material at each point. The validity of this assumption for the dilute open meshworks of most biopolymer gels has been experimentally tested by embedding micron diameter fluorescent beads within the networks formed by fibrin and quantifying their displacements as the macroscopic samples are deformed in a rheometer. Measures of non-affine deformation are small at small strains and decrease as strain increases and the sample stiffens. These results are consistent with the entropic model for non-linear elasticity of semiflexible polymer networks and show that strain-stiffening does not require non-affine deformations.

Alignments of the galaxies in and around the Virgo cluster with the local velocity shear

International Nuclear Information System (INIS)

Lee, Jounghun; Rey, Soo Chang; Kim, Suk

2014-01-01

Observational evidence is presented for the alignment between the cosmic sheet and the principal axis of the velocity shear field at the position of the Virgo cluster. The galaxies in and around the Virgo cluster from the Extended Virgo Cluster Catalog that was recently constructed by Kim et al. are used to determine the direction of the local sheet. The peculiar velocity field reconstructed from the Sloan Digital Sky Survey Data Release 7 is analyzed to estimate the local velocity shear tensor at the Virgo center. Showing first that the minor principal axis of the local velocity shear tensor is almost parallel to the direction of the line of sight, we detect a clear signal of alignment between the positions of the Virgo satellites and the intermediate principal axis of the local velocity shear projected onto the plane of the sky. Furthermore, the dwarf satellites are found to appear more strongly aligned than their normal counterparts, which is interpreted as an indication of the following. (1) The normal satellites and the dwarf satellites fall in the Virgo cluster preferentially along the local filament and the local sheet, respectively. (2) The local filament is aligned with the minor principal axis of the local velocity shear while the local sheet is parallel to the plane spanned by the minor and intermediate principal axes. Our result is consistent with the recent numerical claim that the velocity shear is a good tracer of the cosmic web.

Shear zone nucleation and deformation transient: effect of heterogeneities and loading conditions in experimentally deformed calcite

Science.gov (United States)

Morales, L. F. G.; Rybacki, E.; Dresen, G. H.; Kilian, R.

2015-12-01

In the Earth's middle to lower crust, strain is frequently localized along ductile shear zones, which commonly nucleate at structural and material heterogeneities. To investigate shear zone nucleation and development due to heterogeneities, we performed constant strain-rate (CSR) and constant stress (CS) simple shear (torsion) deformation experiments on Carrara marble samples containing weak (limestone) inclusions. The experiments were conducted in a Paterson-type gas deformation apparatus at 900 °C temperature and 400 MPa confining pressure and maximum bulk shear strains of 3. Peak shear stress was about 20 MPa for all the samples, followed by smooth weakening and steady state behavior. The strain is predominantly localized in the host marble within the process zone in front of the inclusion, defined by a zone of intense grain size reduction due to dynamic recrystallization. In CS tests a narrow shear zone developed in front of the inclusion, whereas in CSR experiments the deformation is more heterogeneously distributed, up to g=3.. In the later, secondary foliations oblique to the process zone and alternating thin, high-strain layers are common. In samples deformed at the same shear strain (g=1), the average recrystallized grain size in the process zone is similar for CS and CSR conditions. Crystallographic preferred orientation (CPO) measurements shows that different grain sizes have slightly different CPO patterns. CPO strength varies for different grain sizes, with a CPO strength peak between 40-50 μm, decreasing progressively within smaller grain size, but with secondary peaks for different coarse-grained sizes. Our observations suggest that the initial formation and transient deformation of shear zones is strongly affected by loading conditions.

Local strains in waste tank deflagration analysis

International Nuclear Information System (INIS)

Bryan, B.J.; Flanders, H.E. Jr.

1993-01-01

In recent years extensive effort has been expended to qualify buried nuclear waste storage tanks under accident conditions. One of these conditions is deflagration of the combustible gases which may build up over time. While much work has been done to calculate the general strain state, less effort has been made to address the local strains at structural discontinuities. An analytical method is presented for calculating these local strains and combining them with the general strain state. A closed form solution of the local strains is compared to a finite element solution

Numerical simulation of systems of shear bands in ductile metal with inclusions

Science.gov (United States)

Plohr, Jeeyeon

2017-06-01

We develop a method for numerical simulations of high strain-rate loading of mesoscale samples of ductile metal with inclusions. Because of its small-scale inhomogeneity, the composite material is prone to localized shear deformation. This method employs the Generalized Method of Cells to ensure that the micro mechanical behavior of the metal and inclusions is reflected properly in the behavior of the composite at the mesoscale. To find the effective plastic strain rate when shear bands are present, we extend and apply the analytic and numerical analysis of shear bands of Glimm, Plohr, and Sharp. Our tests of the method focus on the stress/strain response in uniaxial-strain flow, both compressive and tensile, of depleted uranium metal containing silicon carbide inclusions. In results, we verify the elevated temperature and thermal softening at shear bands in our simulations of pure DU and DU/SiC composites. We also note that in composites, due the asymmetry caused by the inclusions, shear band form at different times in different subcells. In particular, in the subcells near inclusions, shear band form much earlier than they do in pure DU.

Spectral calculations for pressure-velocity and pressure-strain correlations in homogeneous shear turbulence

Science.gov (United States)

Dutta, Kishore

2018-02-01

Theoretical analyses of pressure related turbulent statistics are vital for a reliable and accurate modeling of turbulence. In the inertial subrange of turbulent shear flow, pressure-velocity and pressure-strain correlations are affected by anisotropy imposed at large scales. Recently, Tsuji and Kaneda (2012 J. Fluid Mech. 694 50) performed a set of experiments on homogeneous shear flow, and estimated various one-dimensional pressure related spectra and the associated non-dimensional universal numbers. Here, starting from the governing Navier-Stokes dynamics for the fluctuating velocity field and assuming the anisotropy at inertial scales as a weak perturbation of an otherwise isotropic dynamics, we analytically derive the form of the pressure-velocity and pressure-strain correlations. The associated universal numbers are calculated using the well-known renormalization-group results, and are compared with the experimental estimates of Tsuji and Kaneda. Approximations involved in the perturbative calculations are discussed.

Introduction to the viewpoint set on shear bands

International Nuclear Information System (INIS)

Hutchinson, J.W.

1984-01-01

Recent work aimed at improving our understanding of shear banding and flow localization as modes of deformation and failure is summarized in the six viewpoint articles which follow. For the most part, the emphasis here is on the observation and analysis of shear banding in metals, but active efforts are also underway to understand the role of shear bands in the deformation and failure of soils and rocks. There is a tendency to regard shear bands as a failure mode, as indeed they often are. But extensive straining under highly constrained conditions such as rolling can give rise to profuse flow localization into shear bands which can be regarded as microscopic in the sense that their extent is on the scale of the grains rather than the overall dimensions of the block of material being deformed. Hatherly and Malin describe in detail the observation of such bands and emphasize that they should be considered as a mode of deformation under these circumstances. They relate the formation of the bands to microstructural aspects and discuss their role in the development of recrystallization textures. It will be clear from reading the articles in this viewpoint set that the beginnings of a quantitative theory of shear banding is in place. Continued progress will require parallel developments in constitutive theory and experimental observation. Moreover, basic questions remain to be explored related to the spatial development of the shear bands, their mutual interaction, their development into a failure mode, and how these are influenced by factors such as overall deformational constraint, rate of straining, and temperature

Effects of texture on shear band formation in plane strain tension/compression and bending

DEFF Research Database (Denmark)

Kuroda, M.; Tvergaard, Viggo

2007-01-01

In this study, effects of typical texture components observed in rolled aluminum alloy sheets on shear band formation in plane strain tension/compression and bending are systematically studied. The material response is described by a generalized Taylor-type polycrystal model, in which each grain ...... shear band formation in bent specimens is compared to that in the tension/compression problem. Finally, the present results are compared to previous related studies, and the efficiency of the present method for materials design in future is discussed....

Numerical simulation of systems of shear bands in ductile metal with inclusions

Energy Technology Data Exchange (ETDEWEB)

Plohr, JeeYeon N., E-mail: jplohr@lanl.gov; Plohr, Bradley J. [Los Alamos National Laboratory, Theoretical Division, Los Alamos, NM 87545 (United States)

2016-02-15

We develop a method for numerical simulations of high strain-rate loading of mesoscale samples of ductile metal with inclusions. Because of its small-scale inhomogeneity, the composite material is prone to localized shear deformation (adiabatic shear bands). This method employs the Generalized Method of Cells of Paley and Aboudi [Mech. Materials, vol. 14, pp. 127–139, 1992] to ensure that the micro mechanical behavior of the metal and inclusions is reflected properly in the behavior of the composite at the mesoscale. To find the effective plastic strain rate when shear bands are present, we extend and apply the analytic and numerical analysis of shear bands of Glimm, Plohr, and Sharp [Mech. Materials, vol. 24, pp. 31–41, 1996]. Our tests of the method focus on the stress/strain response in uniaxial-strain flow, both compressive and tensile, of depleted uranium metal containing silicon carbide inclusions. We use the Preston-Tonks-Wallace viscoplasticity model [J. Appl. Phys., vol. 93, pp. 211–220, 2003], which applies to the high strain-rate regime of an isotropic viscoplastic solid. In results, we verify the elevated temperature and thermal softening at shear bands in our simulations of pure DU and DU/SiC composites. We also note that in composites, due the asymmetry caused by the inclusions, shear band form at different times in different subcells. In particular, in the subcells near inclusions, shear band form much earlier than they do in pure DU.

Numerical simulation of systems of shear bands in ductile metal with inclusions

Directory of Open Access Journals (Sweden)

JeeYeon N. Plohr

2016-02-01

Full Text Available We develop a method for numerical simulations of high strain-rate loading of mesoscale samples of ductile metal with inclusions. Because of its small-scale inhomogeneity, the composite material is prone to localized shear deformation (adiabatic shear bands. This method employs the Generalized Method of Cells of Paley and Aboudi [Mech. Materials, vol. 14, pp. 127–139, 1992] to ensure that the micro mechanical behavior of the metal and inclusions is reflected properly in the behavior of the composite at the mesoscale. To find the effective plastic strain rate when shear bands are present, we extend and apply the analytic and numerical analysis of shear bands of Glimm, Plohr, and Sharp [Mech. Materials, vol. 24, pp. 31–41, 1996]. Our tests of the method focus on the stress/strain response in uniaxial-strain flow, both compressive and tensile, of depleted uranium metal containing silicon carbide inclusions. We use the Preston-Tonks-Wallace viscoplasticity model [J. Appl. Phys., vol. 93, pp. 211–220, 2003], which applies to the high strain-rate regime of an isotropic viscoplastic solid. In results, we verify the elevated temperature and thermal softening at shear bands in our simulations of pure DU and DU/SiC composites. We also note that in composites, due the asymmetry caused by the inclusions, shear band form at different times in different subcells. In particular, in the subcells near inclusions, shear band form much earlier than they do in pure DU.

Dynamic localization and shear-induced hopping of particles: A way to understand the rheology of dense colloidal dispersions

International Nuclear Information System (INIS)

Jiang, Tianying; Zukoski, Charles F.

2014-01-01

For decades, attempts have been made to understand the formation of colloidal glasses and gels by linking suspension mechanics to particle properties where details of size, shape, and spatial dependencies of pair potentials present a bewildering array of variables that can be manipulated to achieve observed properties. Despite the range of variables that control suspension properties, one consistent observation is the remarkably similarity of flow properties observed as particle properties are varied. Understanding the underlying origins of the commonality in those behaviors (e.g., shear-thinning with increasing stress, diverging zero shear rate viscosity with increasing volume fraction, development of a dynamic yield stress plateau with increases in volume faction or strength of attraction, development of two characteristic relaxation times probed in linear viscoelasticity, the creation of a rubbery plateau modulus at high strain frequencies, and shear-thickening) remains a challenge. Recently, naïve mode coupling and dynamic localization theories have been developed to capture collective behavior giving rise to formation of colloidal glasses and gels. This approach characterizes suspension mechanics of strongly interacting particles in terms of sluggish long-range particle diffusion modulated by varying particle interactions and volume fraction. These theories capture the scaling of the modulus with the volume fraction and strength of interparticle attraction, the frequency dependence of the moduli at the onset of the gel/glass transition, together with the divergence of the zero shear rate viscosity and cessation of diffusivity for hard sphere systems as close packing is approached. In this study, we explore the generality of the predictions of dynamic localization theory for systems of particles composed of bimodal particle size distributions experiencing weak interactions. We find that the mechanical properties of these suspensions are well captured within

Dynamic localization and shear-induced hopping of particles: A way to understand the rheology of dense colloidal dispersions

Energy Technology Data Exchange (ETDEWEB)

Jiang, Tianying; Zukoski, Charles F., E-mail: czukoski@illinois.edu [Department of Chemical and Biomolecular Engineering, University of Illinois Urbana-Champaign, Urbana, Illinois 61801 (United States)

2014-09-01

For decades, attempts have been made to understand the formation of colloidal glasses and gels by linking suspension mechanics to particle properties where details of size, shape, and spatial dependencies of pair potentials present a bewildering array of variables that can be manipulated to achieve observed properties. Despite the range of variables that control suspension properties, one consistent observation is the remarkably similarity of flow properties observed as particle properties are varied. Understanding the underlying origins of the commonality in those behaviors (e.g., shear-thinning with increasing stress, diverging zero shear rate viscosity with increasing volume fraction, development of a dynamic yield stress plateau with increases in volume faction or strength of attraction, development of two characteristic relaxation times probed in linear viscoelasticity, the creation of a rubbery plateau modulus at high strain frequencies, and shear-thickening) remains a challenge. Recently, naïve mode coupling and dynamic localization theories have been developed to capture collective behavior giving rise to formation of colloidal glasses and gels. This approach characterizes suspension mechanics of strongly interacting particles in terms of sluggish long-range particle diffusion modulated by varying particle interactions and volume fraction. These theories capture the scaling of the modulus with the volume fraction and strength of interparticle attraction, the frequency dependence of the moduli at the onset of the gel/glass transition, together with the divergence of the zero shear rate viscosity and cessation of diffusivity for hard sphere systems as close packing is approached. In this study, we explore the generality of the predictions of dynamic localization theory for systems of particles composed of bimodal particle size distributions experiencing weak interactions. We find that the mechanical properties of these suspensions are well captured within

Diagnosis of Fibrosis and Activity by a Combined Use of Strain and Shear Wave Imaging in Patients with Liver Disease.

Science.gov (United States)

Yada, Norihisa; Tamaki, Nobuhura; Koizumi, Yohei; Hirooka, Masashi; Nakashima, Osamu; Hiasa, Yoichi; Izumi, Namiki; Kudo, Masatoshi

2017-01-01

Performing shear wave imaging is simple, but can be difficult when inflammation, jaundice, and congestion are present. Therefore, the correct diagnosis of liver fibrosis using shear wave imaging alone might be difficult in mild-to-moderate fibrosis cases. Strain imaging can diagnose liver fibrosis without the influence of inflammation. Therefore, the combined use of strain and shear wave imaging (combinational elastography) for cases without jaundice and congestion might be useful for evaluating fibrosis and inflammation. We enrolled consecutive patients with liver disease, without jaundice or liver congestion. Strain and shear wave imaging, blood tests, and liver biopsy were performed on the same day. The liver fibrosis index (LF index) was calculated by strain imaging; real-time tissue elastography, and the shear wave velocity (Vs) was calculated by shear wave imaging. Fibrosis index (F index) and activity index (A index) were calculated as a multiple regression equation for determining hepatic fibrosis and inflammation using histopathological diagnosis as the gold standard. The diagnostic ability of F index for fibrosis and A index for inflammation were compared using LF index and Vs. The total number of enrolled cases was 388. The area under the receiver operating characteristic (AUROC) was 0.87, 0.80, 0.83, and 0.80, at diagnosis of fibrosis stage with an F index of F1 or higher, F2 or higher, F3 or higher, and F4, respectively. The AUROC was 0.94, 0.74, and 0.76 at diagnosis of activity grade with an A index of A1 or higher, A2 or higher, and A3, respectively. The diagnostic ability of F index for liver fibrosis and A index for inflammation was higher than for other conventional diagnostic values. The combined use of strain and shear wave imaging (combinational elastography) might increase the positive diagnosis of liver fibrosis and inflammation. © 2017 S. Karger AG, Basel.

Localization in an anisotropic planar aggregate of spheres

Directory of Open Access Journals (Sweden)

Ragione Luigi La

2017-01-01

Full Text Available We present a micro-mechanical model that is able to predict localization in a sheared planar aggregate of spheres. We assume a non-linear contact law between interacting particles that deform differently from an affine deformation. Equilibrium determines this deviation. The aggregate is isotropically compressed and then sheared so anisotropy develops because of contacts deletion and a non-linear contact law. Because of anisotropy and fluctuations in particles deformation, the resulting macroscopic stiffness tensor, which relates increments in the average stress with increments in the average strain, is characterized by a lack of major symmetry, Aijkl ≠ Aklij. At given shear strain and coordination number it is possible to detemine a plane over which discontinuity in strain occurs; this is identified as localization.

Increasing Accuracy of Tissue Shear Modulus Reconstruction Using Ultrasonic Strain Tensor Measurement

Science.gov (United States)

Sumi, C.

Previously, we developed three displacement vector measurement methods, i.e., the multidimensional cross-spectrum phase gradient method (MCSPGM), the multidimensional autocorrelation method (MAM), and the multidimensional Doppler method (MDM). To increase the accuracies and stabilities of lateral and elevational displacement measurements, we also developed spatially variant, displacement component-dependent regularization. In particular, the regularization of only the lateral/elevational displacements is advantageous for the lateral unmodulated case. The demonstrated measurements of the displacement vector distributions in experiments using an inhomogeneous shear modulus agar phantom confirm that displacement-component-dependent regularization enables more stable shear modulus reconstruction. In this report, we also review our developed lateral modulation methods that use Parabolic functions, Hanning windows, and Gaussian functions in the apodization function and the optimized apodization function that realizes the designed point spread function (PSF). The modulations significantly increase the accuracy of the strain tensor measurement and shear modulus reconstruction (demonstrated using an agar phantom).

Strain hardening in startup shear of long-chain branched polymer solutions.

Science.gov (United States)

Liu, Gengxin; Cheng, Shiwang; Lee, Hyojoon; Ma, Hongwei; Xu, Hongde; Chang, Taihyun; Quirk, Roderic P; Wang, Shi-Qing

2013-08-09

We show for the first time that entangled polymeric liquids containing long-chain branching can exhibit strain hardening upon startup shear. As the significant long-chain branching impedes chain disentanglement, Gaussian coils between entanglements can deform to reach the finite extensibility limit where the intrachain retraction force exceeds the value expected from the usual conformational entropy loss evaluated based on Gaussian chain statistics. The phenomenon is expected to lead to further theoretical understanding.

Doppler optical coherence tomography imaging of local fluid flow and shear stress within microporous scaffolds

Science.gov (United States)

Jia, Yali; Bagnaninchi, Pierre O.; Yang, Ying; Haj, Alicia El; Hinds, Monica T.; Kirkpatrick, Sean J.; Wang, Ruikang K.

2009-05-01

Establishing a relationship between perfusion rate and fluid shear stress in a 3D cell culture environment is an ongoing and challenging task faced by tissue engineers. We explore Doppler optical coherence tomography (DOCT) as a potential imaging tool for in situ monitoring of local fluid flow profiles inside porous chitosan scaffolds. From the measured fluid flow profiles, the fluid shear stresses are evaluated. We examine the localized fluid flow and shear stress within low- and high-porosity chitosan scaffolds, which are subjected to a constant input flow rate of 0.5 ml.min-1. The DOCT results show that the behavior of the fluid flow and shear stress in micropores is strongly dependent on the micropore interconnectivity, porosity, and size of pores within the scaffold. For low-porosity and high-porosity chitosan scaffolds examined, the measured local fluid flow and shear stress varied from micropore to micropore, with a mean shear stress of 0.49+/-0.3 dyn.cm-2 and 0.38+/-0.2 dyn.cm-2, respectively. In addition, we show that the scaffold's porosity and interconnectivity can be quantified by combining analyses of the 3D structural and flow images obtained from DOCT.

The importance of Thermo-Hydro-Mechanical couplings and microstructure to strain localization in 3D continua with application to seismic faults. Part I: Theory and linear stability analysis

Science.gov (United States)

Rattez, Hadrien; Stefanou, Ioannis; Sulem, Jean

2018-06-01

A Thermo-Hydro-Mechanical (THM) model for Cosserat continua is developed to explore the influence of frictional heating and thermal pore fluid pressurization on the strain localization phenomenon. A general framework is presented to conduct a bifurcation analysis for elasto-plastic Cosserat continua with THM couplings and predict the onset of instability. The presence of internal lengths in Cosserat continua enables to estimate the thickness of the localization zone. This is done by performing a linear stability analysis of the system and looking for the selected wavelength corresponding to the instability mode with fastest finite growth coefficient. These concepts are applied to the study of fault zones under fast shearing. For doing so, we consider a model of a sheared saturated infinite granular layer. The influence of THM couplings on the bifurcation state and the shear band width is investigated. Taking representative parameters for a centroidal fault gouge, the evolution of the thickness of the localized zone under continuous shear is studied. Furthermore, the effect of grain crushing inside the shear band is explored by varying the internal length of the constitutive law.

Cross flow response of a cylindrical structure under local shear flow

Directory of Open Access Journals (Sweden)

Yoo-Chul Kim

2009-12-01

Full Text Available The VIV (Vortex-Induced Vibration analysis of a flexible cylindrical structure under locally strong shear flow is presented. The model is made of Teflon and has 9.5m length, 0.0127m diameter, and 0.001m wall thickness. 11 2-dimensional accelerometers are installed along the model. The experiment has been conducted at the ocean engineering basin in the University of Tokyo in which uniform current can be generated. The model is installed at about 30 degree of slope and submerged by almost overall length. Local shear flow is made by superposing uniform current and accelerated flow generated by an impeller. The results of frequency and modal analysis are presented.

Critical Velocity for Shear Localization in A Mature Mylonitic Rock Analogue

Science.gov (United States)

Takahashi, M.; van den Ende, M.; Niemeijer, A. R.; Spiers, C. J.

2016-12-01

Highly localized slip zones, seen within ductile shear zones developed in nature, such as pseudotachylite bands occurring within mylonites, are widely recognized as evidence for earthquake nucleation and/or propagation within and overprinting the ductile regime. To understand brittle/frictional localization processes in ductile shear zones and to connect these to earthquake nucleation and propagation processes, we performed large velocity step-change tests on a brine-saturated, 80:20 (wt. %) halite and muscovite gouge mixture, after forming a mature mylonitic structure through pressure solution creep at low-velocity. The sharp increase in sliding strength that occurs in response to an instantaneous upward velocity-step (direct effect) is an important parameter in determining the potential for and nature of seismic rupture nucleation. We obtained reproducible results regarding low velocity mechanical behavior compared with previous work of Niemeijer and Spiers, [2006], but also obtained new insights into the effects of sudden increases in slip velocity on localization and strength evolution, at velocities above a specific critical velocity Vc ( 20 μm/sec). We found that once a ductile, mylonitic structure has developed in a shear zone, subsequent cataclastic deformation at high velocity (> Vc) is consistently localized in a narrow zone characterized by fine grains of halite aligned in arrays between foliated muscovite Due to this intense localization, structures presumably developed under low velocity conditions were still preserved in large parts of the gouge body. This switch to localized deformation is controlled by the imposed velocity, and becomes most apparent at velocities over Vc. In addition, the direct effect a decreases rapidly when the velocity exceeds Vc. This implies that slip can localize and accelerate towards seismic velocities more or less instantly once Vc is exceeded. Obtaining a measure for Vc in natural faults is therefore of key importance

Mechanisms of strain accommodation in plastically-deformed zircon under simple shear deformation conditions during amphibolite-facies metamorphism

Science.gov (United States)

Kovaleva, Elizaveta; Klötzli, Urs; Wheeler, John; Habler, Gerlinde

2018-02-01

This study documents the strain accommodation mechanisms in zircon under amphibolite-facies metamorphic conditions in simple shear. Microstructural data from undeformed, fractured and crystal-plastically deformed zircon crystals are described in the context of the host shear zone, and evaluated in the light of zircon elastic anisotropy. Our work challenges the existing model of zircon evolution and shows previously undescribed rheological characteristics for this important accessory mineral. Crystal-plastically deformed zircon grains have axis oriented parallel to the foliation plane, with the majority of deformed grains having axis parallel to the lineation. Zircon accommodates strain by a network of stepped low-angle boundaries, formed by switching between tilt dislocations with the slip systems {010} and {110} and rotation axis [001], twist dislocations with the rotation axis [001], and tilt dislocations with the slip system {001} and rotation axis [010]. The slip system {110} is newly described for zircon. Most misorientation axes in plastically-deformed zircon grains are parallel to the XY plane of the sample and have [001] crystallographic direction. Such behaviour of strained zircon lattice is caused by elastic anisotropy that has a direct geometric control on the rheology, deformation mechanisms and dominant slip systems in zircon. Young's modulus and P wave velocity have highest values parallel to zircon [001] axis, indicating that zircon is elastically strong along this direction. Poisson ratio and Shear modulus demonstrate that zircon is also most resistant to shearing along [001]. Thus, [001] axis is the most common rotation axis in zircon. The described zircon behaviour is important to take into account during structural and geochronological investigations of (poly)metamorphic terrains. Geometry of dislocations in zircon may help reconstructing the geometry of the host shear zone(s), large-scale stresses in the crust, and, possibly, the timing of

Effect of shear strain on the α-ε phase transition of iron: a new approach in the rotational diamond anvil cell

International Nuclear Information System (INIS)

Ma Yanzhang; Selvi, Emre; Levitas, Valery I; Hashemi, Javad

2006-01-01

The effect of shear strain on the iron α-ε phase transformation has been studied using a rotational diamond anvil cell (RDAC). The initial transition is observed to take place at the reduced pressure of 10.8 GPa under pressure and shear operation. Complete phase transformation was observed at 15.4 GPa. The rotation of an anvil causes limited pressure elevation and makes the pressure distribution symmetric in the sample chamber before the phase transition. However, it causes a significant pressure increase at the centre of the sample and brings about a large pressure gradient during the phase transformation. The resistance to the phase interface motion is enhanced due to strain hardening during the pressure and shear operations on iron and this further increases the transition pressure. The work of macroscopic shear stress and the work of the pressure and shear stress at the defect tips account for the pressure reduction of the iron phase transition

Relating rheology to geometry in large-scale natural shear zones

Science.gov (United States)

Platt, John

2016-04-01

The geometry and width of the ductile roots of plate boundary scale faults are very poorly understood. Some field and geophysical data suggests widths of tens of km in the lower crust, possibly more in the upper mantle. Other observations suggest they are much narrower. Dip slip shear zones may flatten out and merge into zones of subhorizontal lower crustal or asthenospheric flow. The width of a ductile shear zone is simply related to relative velocity and strain rate. Strain rate is related to stress through the constitutive relationship. Can we constrain the stress, and do we understand the rheology of materials in ductile shear zones? A lot depends on how shear zones are initiated. If they are localized by pre-existing structures, width and/or rheology may be inherited, and we have too many variables. If shear zones are localized primarily by shear heating, initial shear stress has to be very high (> 1 GPa) to overcome conductive heat loss, and very large feedbacks (both positive and negative) make the system highly unstable. Microstructural weakening requires a minimum level of stress to cause deformation and damage in surrounding rock, thereby buffering the stress. Microstructural weakening leads to grain-size sensitive creep, for which we have constitutive laws, but these are complicated by phase mixing in polyphase materials, by viscous anisotropy, by hydration, and by changes in mineral assemblage. Here are some questions that need to be addressed. (1) If grain-size reduction by dynamic recrystallization results in a switch to grain-size sensitive creep (GSSC) in a stress-buffered shear zone, does dynamic recrystallization stop? Does grain growth set in? If grain-size is still controlled by dislocation processes, then the effective stress exponent for GSSC is 4-5, even though the dominant mechanism may be diffusion and/or grain-boundary sliding (GBS). (2) Is phase mixing in ultramylonites primarily a result of GBS + neighbour switching, creep cavitation and

The elastic strain energy of crystallographic shear planes in reduced tungsten trioxide

International Nuclear Information System (INIS)

Iguchi, E.; Tilley, R.J.D.

1977-01-01

Calculations of the elastic strain energy due to crystallographic shear (c.s.) planes lying upon 102, 103 and 001 planes in reduced tungsten trioxide crystals have been made. The cases analysed in detail are for both isolated c.s. planes and for pairs of c.s. planes. These results are used to determine the elastic strain energy per unit volume for crystals containing ordered arrays of c.s. planes. It was found that the magnitude of the elastic strain energy was in the sequence 001 < 102 < 103 and that at relatively small inter-c.s. spacings the curves of elastic strain energy against c.s. plane separation take the form of a series of peaks and valleys. These results are compared with experimental observations of c.s. plane spacings in substantially reduced crystals containing quasi-ordered arrays of c.s. planes and with observations of c.s. plane nucleation and growth in both slightly and more appreciably reduced crystals. It was found that the elastic strain energy plays a significant part in controlling the microstructure of c.s. plane arrays in such cases. (author)

Integrated 3D Geological Modeling to Gain Insight in the Effects of Hydrothermal Alteration on Post-Ore Deformation Style and Strain Localization in the Flin Flon Volcanogenic Massive Sulfide Ore System

Directory of Open Access Journals (Sweden)

Ernst Schetselaar

2017-12-01

Full Text Available 3D geological modeling of lithogeochemical and geological data provides insight into the role of the sulfide ore horizon and associated footwall hydrothermal alteration in localizing shear strain in the Flin Flon volcanogenic massive sulfide deposits, Canada, as deformation evolved from brittle-ductile to ductile regimes during collisional stages of the 1.9–1.8 Ga Trans-Hudson orogeny. 3D spatial characterization of hydrothermal alteration based on the Ishikawa index (AI and normative corundum percentages outline sericite + chlorite-rich high strain zones, consisting of Al-enriched and Na-depleted felsic and mafic volcanic rocks in the footwall of the sulfide ore horizon. The hydrothermal vent complex, from which these sheared alteration zones originated, was stacked together with the ore horizon by W-vergent thrust faults during an early collisional deformation regime, imbricating molasse-type clastic sediments with the ore-hosting volcanic and volcaniclastic rocks of the Flin Flon arc assemblage. Chlorite-rich planar zones marked by high values of the Carbonate–chlorite–pyrite index (CCPI are laterally more extensive and outline a later system of ductile shear zones, in which phyllosilicates, quartz and chalcopyrite in stringer zones localized shear strain and enhanced transposition of the hydrothermal vent stockwork. The contrasting deformation styles of these two thrusting events and their localization within the ore horizon and hydrothermal vent stockwork have important implications for vectoring towards undiscovered ore in this mature mining camp that are possibly also relevant to other strongly deformed VMS ore systems.

Dynamic Shear Deformation and Failure of Ti-6Al-4V and Ti-5Al-5Mo-5V-1Cr-1Fe Alloys.

Science.gov (United States)

Ran, Chun; Chen, Pengwan

2018-01-05

To study the dynamic shear deformation and failure properties of Ti-6Al-4V (Ti-64) alloy and Ti-5Al-5Mo-5V-1Cr-1Fe (Ti-55511) alloy, a series of forced shear tests on flat hat shaped (FHS) specimens for the two investigated materials was performed using a split Hopkinson pressure bar setup. The evolution of shear deformation was monitored by an ultra-high-speed camera (Kirana-05M). Localized shear band is induced in the two investigated materials under forced shear tests. Our results indicate that severe strain localization (adiabatic shear) is accompanied by a loss in the load carrying capacity, i.e., by a sudden drop in loading. Three distinct stages can be identified using a digital image correlation technique for accurate shear strain measurement. The microstructural analysis reveals that the dynamic failure mechanisms for Ti-64 and Ti-55511 alloys within the shear band are of a cohesive and adhesive nature, respectively.

estimation of shear strength parameters of lateritic soils using

African Journals Online (AJOL)

user

... a tool to estimate the. Nigerian Journal of Technology (NIJOTECH). Vol. ... modeling tools for the prediction of shear strength parameters for lateritic ... 2.2 Geotechnical Analysis of the Soils ... The back propagation learning algorithm is the most popular and ..... [10] Alsaleh, M. I., Numerical modeling for strain localization in ...

Influence of equilibrium shear flow on peeling-ballooning instability and edge localized mode crash

International Nuclear Information System (INIS)

Xi, P. W.; Xu, X. Q.; Wang, X. G.; Xia, T. Y.

2012-01-01

The E × B shear flow plays a dual role on peeling-ballooning modes and their subsequently triggered edge localized mode (ELM) crashes. On one hand, the flow shear can stabilize high-n modes and twist the mode in the poloidal direction, constraining the mode's radial extent and reducing the size of the corresponding ELM. On the other hand, the shear flow also introduces the Kelvin-Helmholtz drive, which can destabilize peeling-ballooning modes. The overall effect of equilibrium shear flow on peeling-ballooning modes and ELM crashes depends on the competition between these two effects. When the flow shear is either small or very large, it can reduce ELM size. However, for moderate values of flow shear, the destabilizing effect from the Kelvin-Helmholtz term is dominant and leads to larger ELM crashes.

Magnetism and Raman Spectroscopy of Pristine and Hydrogenated TaSe2 Monolayer tuned by Tensile and Pure Shear Strain

Science.gov (United States)

Chowdhury, Sugata; Simpson, Jeffrey; Einstein, T. L.; Walker, Angela R. Hight

2D-materials with controllable optical, electronic and magnetic properties are desirable for novel nanodevices. Here we studied these properties for both pristine and hydrogenated TaSe2 (TaSe2-H) monolayer (ML) in the framework of DFT using the PAW method. We considered uniaxial and biaxial tensile strain, as well as shear strain along the basal planes in the range between 1% and 16%. Previous theoretical works (e.g.) considered only symmetrical biaxial tensile. Pristine ML is ferromagnetic for uniaxial tensile strain along ◯ or ŷ. For tensile strain in ŷ, the calculated magnetic moments of the Ta atoms are twice those for the same strain in ◯. Under pure shear strain (expansion along ŷ and compression along ◯), a pristine ML is ferromagnetic, but becomes non-magnetic when the strain directions are interchanged. Due to carrier-mediated double-exchange, the pristine ML is ferromagnetic when the Se-Ta-Se bond angle is < 82° and the ML thickness is < 3.25Å. We find that all Raman-active phonon modes show obvious red-shifting due to bond elongation and the E2 modes degeneracy is lifted as strain increases. For a TaSe2-H ML, the same trends were observed. Results show the ability to tune the properties of 2D-materials.

Shear melting and high temperature embrittlement: theory and application to machining titanium.

Science.gov (United States)

Healy, Con; Koch, Sascha; Siemers, Carsten; Mukherji, Debashis; Ackland, Graeme J

2015-04-24

We describe a dynamical phase transition occurring within a shear band at high temperature and under extremely high shear rates. With increasing temperature, dislocation deformation and grain boundary sliding are supplanted by amorphization in a highly localized nanoscale band, which allows for massive strain and fracture. The mechanism is similar to shear melting and leads to liquid metal embrittlement at high temperature. From simulation, we find that the necessary conditions are lack of dislocation slip systems, low thermal conduction, and temperature near the melting point. The first two are exhibited by bcc titanium alloys, and we show that the final one can be achieved experimentally by adding low-melting-point elements: specifically, we use insoluble rare earth metals (REMs). Under high shear, the REM becomes mixed with the titanium, lowering the melting point within the shear band and triggering the shear-melting transition. This in turn generates heat which remains localized in the shear band due to poor heat conduction. The material fractures along the shear band. We show how to utilize this transition in the creation of new titanium-based alloys with improved machinability.

Deformation and failure response of 304L stainless steel SMAW joint under dynamic shear loading

International Nuclear Information System (INIS)

Lee, Woei-Shyan; Cheng, J.-I.; Lin, C.-F.

2004-01-01

The dynamic shear deformation behavior and fracture characteristics of 304L stainless steel shielded metal arc welding (SMAW) joint are studied experimentally with regard to the relations between mechanical properties and strain rate. Thin-wall tubular specimens are deformed at room temperature under strain rates in the range of 8 x 10 2 to 2.8 x 10 3 s -1 using a torsional split-Hopkinson bar. The results indicate that the strain rate has a significant influence on the mechanical properties and fracture response of the tested SMAW joints. It is found that the flow stress, total shear strain to failure, work hardening rate and strain rate sensitivity all increase with increasing strain rate, but that the activation volume decreases. The observed dynamic shear deformation behavior is modeled using the Kobayashi-Dodd constitutive law, and it is shown that the predicted results are in good agreement with the experimental data. Fractographic analysis using scanning electron microscopy reveals that the tested specimens all fracture within their fusion zones, and that the primary failure mechanism is one of the extensive localized shearing. The fracture surfaces are characterized by the presence of many dimples. A higher strain rate tends to reduce the size of the dimples and to increase their density. The observed fracture features are closely related to the preceding flow behavior

Finite strain analysis of metavolcanics and metapyroclastics in gold-bearing shear zone of the Dungash area, Central Eastern Desert, Egypt

Science.gov (United States)

Kassem, Osama M. K.; Abd El Rahim, Said H.

2014-11-01

The Dungash gold mine area is situated in an EW-trending quartz vein along a shear zone in metavolcanic and metasedimentary host rocks in the Eastern Desert of Egypt. These rocks are associated with the major geologic structures, which are attributed to various deformational stages of the Neoproterozoic basement rocks. Field geology, finite strain and microstructural analyses were carried out and the relation-ships between the lithological contacts and major/minor structures have been studied. The R f/ϕ and Fry methods were applied on the metavolcano-sedimentary and metapyroclastic samples from 5 quartz veins samples, 7 metavolcanics samples, 3 metasedimentary samples and 4 metapyroclastic samples in Dungash area. Finite-strain data show that a low to moderate range of deformation of the metavolcano-sedimentary samples and axial ratios in the XZ section range from 1.70 to 4.80 for the R f/ϕ method and from 1.65 to 4.50 for the Fry method. We conclude that finite strain in the deformed rocks is of the same order of magnitude for all units of metavolcano-sedimentary rocks. Furthermore, the contact between principal rock units is sheared in the Dungash area under brittle to semi-ductile deformation conditions. In this case, the accumulated finite strain is associated with the deformation during thrusting to assemble nappe structure. It indicates that the sheared contacts have been formed during the accumulation of finite strain.

Shear Melting of a Colloidal Glass

Science.gov (United States)

Eisenmann, Christoph; Kim, Chanjoong; Mattsson, Johan; Weitz, David A.

2010-01-01

We use confocal microscopy to explore shear melting of colloidal glasses, which occurs at strains of ˜0.08, coinciding with a strongly non-Gaussian step size distribution. For larger strains, the particle mean square displacement increases linearly with strain and the step size distribution becomes Gaussian. The effective diffusion coefficient varies approximately linearly with shear rate, consistent with a modified Stokes-Einstein relationship in which thermal energy is replaced by shear energy and the length scale is set by the size of cooperatively moving regions consisting of ˜3 particles.

Development of local shear bands and orientation gradients in fcc polycrystals

International Nuclear Information System (INIS)

Beaudoin, A.J. Jr.; Mecking, H.; Kocks, U.F.

1995-01-01

A finite element formulation which derives constitutive response from crystal plasticity theory is used to examine localized deformation in fcc polycrystals. The polycrystals are simple, idealized arrangements of grains. Localized deformations within individual grains lead to the development of domains that are separated by boundaries of high misorientation. Shear banding is seen to occur on a microscopic scale of grain dimensions. The important consequences of these simulations are that the predicted local inhomogeneities are meeting various requirements which make them possible nucleation sites for recrystallization

Analytical solution for shear bands in cold-rolled 1018 steel

Science.gov (United States)

Voyiadjis, George Z.; Almasri, Amin H.; Faghihi, Danial; Palazotto, Anthony N.

2012-06-01

Cold-rolled 1018 (CR-1018) carbon steel has been well known for its susceptibility to adiabatic shear banding under dynamic loadings. Analysis of these localizations highly depends on the selection of the constitutive model. To deal with this issue, a constitutive model that takes temperature and strain rate effect into account is proposed. The model is motivated by two physical-based models: the Zerilli and Armstrong and the Voyiadjis and Abed models. This material model, however, incorporates a simple softening term that is capable of simulating the softening behavior of CR-1018 steel. Instability, localization, and evolution of adiabatic shear bands are discussed and presented graphically. In addition, the effect of hydrostatic pressure is illustrated.

Shear of ordinary and elongated granular mixtures

Science.gov (United States)

Hensley, Alexander; Kern, Matthew; Marschall, Theodore; Teitel, Stephen; Franklin, Scott

2015-03-01

We present an experimental and computational study of a mixture of discs and moderate aspect-ratio ellipses under two-dimensional annular planar Couette shear. Experimental particles are cut from acrylic sheet, are essentially incompressible, and constrained in the thin gap between two concentric cylinders. The annular radius of curvature is much larger than the particles, and so the experiment is quasi-2d and allows for arbitrarily large pure-shear strains. Synchronized video cameras and software identify all particles and track them as they move from the field of view of one camera to another. We are particularly interested in the global and local properties as the mixture ratio of discs to ellipses varies. Global quantities include average shear rate and distribution of particle species as functions of height, while locally we investigate the orientation of the ellipses and non-affine events that can be characterized as shear transformational zones or possess a quadrupole signature observed previously in systems of purely circular particles. Discrete Element Method simulations on mixtures of circles and spherocylinders extend the study to the dynamics of the force network and energy dissipated as the system evolves. Supported by NSF CBET #1243571 and PRF #51438-UR10.

Experimental study of shear rate dependence in perpetually sheared granular matter

Science.gov (United States)

Liu, Sophie Yang; Guillard, François; Marks, Benjy; Rognon, Pierre; Einav, Itai

2017-06-01

We study the shear behaviour of various granular materials by conducting novel perpetual simple shear experiments over four orders of magnitude of relatively low shear rates. The newly developed experimental apparatus employed is called "3D Stadium Shear Device" which is an extended version of the 2D Stadium Shear Device [1]. This device is able to provide a non-radial dependent perpetual shear flow and a nearly linear velocity profile between two oppositely moving shear walls. Using this device, we are able to test a large variety of granular materials. Here, we demonstrate the applicability of the device on glass beads (diameter 1 mm, 3 mm, and 14 mm) and rice. We particularly focus on studying these materials at very low inertial number I ranging from 10-6 to 10-2. We find that, within this range of I, the friction coefficient μ of glass beads has no shear rate dependence. A particularly appealing observation comes from testing rice, where the attainment of critical state develops under much longer duration than in other materials. Initially during shear we find a value of μ similar to that found for glass beads, but with time this value decreases gradually towards the asymptotic critical state value. The reason, we believe, lies in the fact that rice grains are strongly elongated; hence the time to achieve the stable μ is primarily controlled by the time for particles to align themselves with respect to the shear walls. Furthermore, the initial packing conditions of samples also plays a role in the evolution of μ when the shear strain is small, but that impact will eventually be erased after sufficient shear strain.

Seismic anisotropy in localized shear zones versus distributed tectonic fabrics: examples from geologic and seismic observations in western North America and the European Alps

Science.gov (United States)

Mahan, Kevin H.; Schulte-Pelkum, Vera; Condit, Cailey; Leydier, Thomas; Goncalves, Philippe; Raju, Anissha; Brownlee, Sarah; Orlandini, Omero F.

2017-04-01

amphibolite-facies (0.9-1.0 GPa, 700 °C) mafic metagabbro from Precambrian exposures in Montana (USA) and in greenschist-facies (0.7-0.8 GPa, 450-500 °C) metagranites from the External Crystalline Massifs of the European Central Alps. The shear zones are characterized by strain gradients from undeformed coarse-grained protoliths to very fine grained ultramylonite, and by microstructures dominated by CPO-producing deformation mechanisms in the protomylonite and CPO-weakening mechanisms such as dissolution-precipitation creep and grain boundary sliding in the ultramylonite. In the mafic mylonites, the result is a lower seismic anisotropy ( 2%) in the core of the shear zones despite a well-developed hornblende shape-preferred orientation. Preliminary observations of these examples suggest that marginal gradients may contribute as much or more to the bulk anisotropy signal compared to the higher strained cores of these structures. If true, a similar effect could explain some otherwise puzzling anisotropy studies of larger scale shear zones such as from the Himalaya where anisotropy tilt proximal to the Main Himalayan Thrust is notably steeper than expected. In conclusion, while some anisotropy studies of crustal scale deformation patterns are relatively straightforward, others will require careful consideration of the limitations and potential future improvements to seismic detection methods, including ground truthing based on samples and exposures as well as a better understanding of physical processes involved in deformation localization.

Effect of shear connectors on local buckling and composite action in steel concrete composite walls

International Nuclear Information System (INIS)

Zhang, Kai; Varma, Amit H.; Malushte, Sanjeev R.; Gallocher, Stewart

2014-01-01

Steel concrete composite (SC) walls are being used for the third generation nuclear power plants, and also being considered for small modular reactors. SC walls consist of thick concrete walls with exterior steel faceplates serving as reinforcement. These steel faceplates are anchored to the concrete infill using shear connectors, for example, headed steel studs. The steel faceplate thickness (t p ) and yield stress (F y ), and the shear connector spacing (s), stiffness (k s ), and strength (Q n ) determine: (a) the level of composite action between the steel plates and the concrete infill, (b) the development length of steel faceplates, and (c) the local buckling of the steel faceplates. Thus, the shear connectors have a significant influence on the behavior of composite SC walls, and should be designed accordingly. This paper presents the effects of shear connector design on the level of composite action and development length of steel faceplates in SC walls. The maximum steel plate slenderness, i.e., ratio of shear connector spacing-to-plate thickness (s/t p ) ratio to prevent local buckling before yielding is also developed based on the existing experimental database and additional numerical analysis

Effect of shear connectors on local buckling and composite action in steel concrete composite walls

Energy Technology Data Exchange (ETDEWEB)

Zhang, Kai, E-mail: kai-zh@purdue.edu [School of Civil Engineering, Purdue University, West Lafayette, IN (United States); Varma, Amit H., E-mail: ahvarma@purdue.edu [School of Civil Engineering, Purdue University, West Lafayette, IN (United States); Malushte, Sanjeev R., E-mail: smalusht@bechtel.com [Bechtel Power Corporation, Frederick, MD (United States); Gallocher, Stewart, E-mail: stewart.gallocher@steelbricks.com [Modular Walling Systems Ltd., Glasgow (United Kingdom)

2014-04-01

Steel concrete composite (SC) walls are being used for the third generation nuclear power plants, and also being considered for small modular reactors. SC walls consist of thick concrete walls with exterior steel faceplates serving as reinforcement. These steel faceplates are anchored to the concrete infill using shear connectors, for example, headed steel studs. The steel faceplate thickness (t{sub p}) and yield stress (F{sub y}), and the shear connector spacing (s), stiffness (k{sub s}), and strength (Q{sub n}) determine: (a) the level of composite action between the steel plates and the concrete infill, (b) the development length of steel faceplates, and (c) the local buckling of the steel faceplates. Thus, the shear connectors have a significant influence on the behavior of composite SC walls, and should be designed accordingly. This paper presents the effects of shear connector design on the level of composite action and development length of steel faceplates in SC walls. The maximum steel plate slenderness, i.e., ratio of shear connector spacing-to-plate thickness (s/t{sub p}) ratio to prevent local buckling before yielding is also developed based on the existing experimental database and additional numerical analysis.

Effect of nitrogen concentration and temperature on the critical resolved shear stress and strain rate sensitivity of vanadium

International Nuclear Information System (INIS)

Rehbein, D.K.

1980-08-01

The critical resolved shear stress and strain rate sensitivity were measured over the temperature range from 77 to 400 0 K for vanadium-nitrogen alloys containing from 0.0004 to 0.184 atom percent nitrogen. These properties were found to be strongly dependent on both the nitrogen concentration and temperature. The following observations were seen in this investigation: the overall behavior of the alloys for the temperature and concentration range studied follows a form similar to that predicted; the concentration dependence of the critical resolved shear stress after subtracting the hardening due to the pure vanadium lattice obeys Labusch's c/sup 2/3/ relationship above 200 0 K and Fleischer's c/sup 1/2/ relationship below 200 0 K; the theoretical predictions of Fleischer's model for the temperature dependence of the critical resolved shear stress are in marked disagreement with the behavior found; and the strain rate sensitivity, par. delta tau/par. deltaln γ, exhibits a peak at approximately 100 0 K that decreases in height as the nitrogen concentration increases. A similar peak has been observed in niobium by other investigators but the effect of concentration on the peak height is quite different

Seismic cycle feedbacks in a mid-crustal shear zone

Science.gov (United States)

Melosh, Benjamin L.; Rowe, Christie D.; Gerbi, Christopher; Smit, Louis; Macey, Paul

2018-07-01

Mid-crustal fault rheology is controlled by alternating brittle and plastic deformation mechanisms, which cause feedback cycles that influence earthquake behavior. Detailed mapping and microstructural observations in the Pofadder Shear Zone (Namibia and South Africa) reveal a lithologically heterogeneous shear zone core with quartz-rich mylonites and ultramylonites, plastically overprinted pseudotachylyte and active shear folds. We present evidence for a positive feedback cycle in which coseismic grain size reduction facilitates active shear folding by enhancing competency contrasts and promoting crystal plastic flow. Shear folding strengthens a portion of a shear zone by limb rotation, focusing deformation and promoting plastic flow or brittle slip in resulting areas of localized high stress. Using quartz paleopiezometry, we estimate strain and slip rates consistent with other studies of exhumed shear zones and modern plate boundary faults, helping establish the Pofadder Shear Zone as an ancient analogue to modern, continental-scale, strike-slip faults. This feedback cycle influences seismicity patterns at the scale of study (10s of meters) and possibly larger scales as well, and contributes to bulk strengthening of the brittle-plastic transition on modern plate boundary faults.

Coexistence and transition between shear zones in slow granular flows.

Science.gov (United States)

Moosavi, Robabeh; Shaebani, M Reza; Maleki, Maniya; Török, János; Wolf, Dietrich E; Losert, Wolfgang

2013-10-04

We report experiments on slow granular flows in a split-bottom Couette cell that show novel strain localization features. Nontrivial flow profiles have been observed which are shown to be the consequence of simultaneous formation of shear zones in the bulk and at the boundaries. The fluctuating band model based on a minimization principle can be fitted to the experiments over a large variation of morphology and filling height with one single fit parameter, the relative friction coefficient μ(rel) between wall and bulk. The possibility of multiple shear zone formation is controlled by μ(rel). Moreover, we observe that the symmetry of an initial state, with coexisting shear zones at both side walls, breaks spontaneously below a threshold value of the shear velocity. A dynamical transition between two asymmetric flow states happens over a characteristic time scale which depends on the shear strength.

Continuous shear - a method for studying material elements passing a stationary shear plane

DEFF Research Database (Denmark)

Lindegren, Maria; Wiwe, Birgitte; Wanheim, Tarras

2003-01-01

circumferential groove. Normally shear in metal forming processes is of another nature, namely where the material elements move through a stationary shear zone, often of small width. In this paper a method enabling the simulation of this situation is presented. A tool for continuous shear has beeen manufactured...... and tested with AlMgSil and copper. The sheared material has thereafter been tested n plane strain compression with different orientation concerning the angle between the shear plane and the compression direction....

Influence of equilibrium shear flow in the parallel magnetic direction on edge localized mode crash

Energy Technology Data Exchange (ETDEWEB)

Luo, Y.; Xiong, Y. Y. [College of Physical Science and Technology, Sichuan University, 610064 Chengdu (China); Chen, S. Y., E-mail: sychen531@163.com [College of Physical Science and Technology, Sichuan University, 610064 Chengdu (China); Key Laboratory of High Energy Density Physics and Technology of Ministry of Education, Sichuan University, Chengdu 610064 (China); Southwestern Institute of Physics, Chengdu 610041 (China); Huang, J.; Tang, C. J. [College of Physical Science and Technology, Sichuan University, 610064 Chengdu (China); Key Laboratory of High Energy Density Physics and Technology of Ministry of Education, Sichuan University, Chengdu 610064 (China)

2016-04-15

The influence of the parallel shear flow on the evolution of peeling-ballooning (P-B) modes is studied with the BOUT++ four-field code in this paper. The parallel shear flow has different effects in linear simulation and nonlinear simulation. In the linear simulations, the growth rate of edge localized mode (ELM) can be increased by Kelvin-Helmholtz term, which can be caused by the parallel shear flow. In the nonlinear simulations, the results accord with the linear simulations in the linear phase. However, the ELM size is reduced by the parallel shear flow in the beginning of the turbulence phase, which is recognized as the P-B filaments' structure. Then during the turbulence phase, the ELM size is decreased by the shear flow.

Experimental study of shear rate dependence in perpetually sheared granular matter

Directory of Open Access Journals (Sweden)

Liu Sophie Yang

2017-01-01

Full Text Available We study the shear behaviour of various granular materials by conducting novel perpetual simple shear experiments over four orders of magnitude of relatively low shear rates. The newly developed experimental apparatus employed is called “3D Stadium Shear Device” which is an extended version of the 2D Stadium Shear Device [1]. This device is able to provide a non-radial dependent perpetual shear flow and a nearly linear velocity profile between two oppositely moving shear walls. Using this device, we are able to test a large variety of granular materials. Here, we demonstrate the applicability of the device on glass beads (diameter 1 mm, 3 mm, and 14 mm and rice. We particularly focus on studying these materials at very low inertial number I ranging from 10−6 to 10−2. We find that, within this range of I, the friction coefficient μ of glass beads has no shear rate dependence. A particularly appealing observation comes from testing rice, where the attainment of critical state develops under much longer duration than in other materials. Initially during shear we find a value of μ similar to that found for glass beads, but with time this value decreases gradually towards the asymptotic critical state value. The reason, we believe, lies in the fact that rice grains are strongly elongated; hence the time to achieve the stable μ is primarily controlled by the time for particles to align themselves with respect to the shear walls. Furthermore, the initial packing conditions of samples also plays a role in the evolution of μ when the shear strain is small, but that impact will eventually be erased after sufficient shear strain.

Influence of Additive Manufactured Scaffold Architecture on the Distribution of Surface Strains and Fluid Flow Shear Stresses and Expected Osteochondral Cell Differentiation.

Science.gov (United States)

Hendrikson, Wim J; Deegan, Anthony J; Yang, Ying; van Blitterswijk, Clemens A; Verdonschot, Nico; Moroni, Lorenzo; Rouwkema, Jeroen

2017-01-01

Scaffolds for regenerative medicine applications should instruct cells with the appropriate signals, including biophysical stimuli such as stress and strain, to form the desired tissue. Apart from that, scaffolds, especially for load-bearing applications, should be capable of providing mechanical stability. Since both scaffold strength and stress-strain distributions throughout the scaffold depend on the scaffold's internal architecture, it is important to understand how changes in architecture influence these parameters. In this study, four scaffold designs with different architectures were produced using additive manufacturing. The designs varied in fiber orientation, while fiber diameter, spacing, and layer height remained constant. Based on micro-CT (μCT) scans, finite element models (FEMs) were derived for finite element analysis (FEA) and computational fluid dynamics (CFD). FEA of scaffold compression was validated using μCT scan data of compressed scaffolds. Results of the FEA and CFD showed a significant impact of scaffold architecture on fluid shear stress and mechanical strain distribution. The average fluid shear stress ranged from 3.6 mPa for a 0/90 architecture to 6.8 mPa for a 0/90 offset architecture, and the surface shear strain from 0.0096 for a 0/90 offset architecture to 0.0214 for a 0/90 architecture. This subsequently resulted in variations of the predicted cell differentiation stimulus values on the scaffold surface. Fluid shear stress was mainly influenced by pore shape and size, while mechanical strain distribution depended mainly on the presence or absence of supportive columns in the scaffold architecture. Together, these results corroborate that scaffold architecture can be exploited to design scaffolds with regions that guide specific tissue development under compression and perfusion. In conjunction with optimization of stimulation regimes during bioreactor cultures, scaffold architecture optimization can be used to improve

Haptic Edge Detection Through Shear

Science.gov (United States)

Platkiewicz, Jonathan; Lipson, Hod; Hayward, Vincent

2016-03-01

Most tactile sensors are based on the assumption that touch depends on measuring pressure. However, the pressure distribution at the surface of a tactile sensor cannot be acquired directly and must be inferred from the deformation field induced by the touched object in the sensor medium. Currently, there is no consensus as to which components of strain are most informative for tactile sensing. Here, we propose that shape-related tactile information is more suitably recovered from shear strain than normal strain. Based on a contact mechanics analysis, we demonstrate that the elastic behavior of a haptic probe provides a robust edge detection mechanism when shear strain is sensed. We used a jamming-based robot gripper as a tactile sensor to empirically validate that shear strain processing gives accurate edge information that is invariant to changes in pressure, as predicted by the contact mechanics study. This result has implications for the design of effective tactile sensors as well as for the understanding of the early somatosensory processing in mammals.

Analysis of local microstructure after shear creep deformation of a fine-grained duplex {gamma}-TiAl alloy

Energy Technology Data Exchange (ETDEWEB)

Peter, D., E-mail: dennis.peter@rub.de [Institute for Materials, Ruhr University Bochum, Universitaetsstrasse 150, 44801 Bochum (Germany); Viswanathan, G.B. [Institute for Materials, Ruhr University Bochum, Universitaetsstrasse 150, 44801 Bochum (Germany)] [Air Force Research Laboratory, Wright-Patterson AFB, OH 45433 (United States); Dlouhy, A. [Institute of Physics of Materials, Academy of Sciences of the Czech Republic, 61662 Brno, Zizkova 22 (Czech Republic); Eggeler, G. [Institute for Materials, Ruhr University Bochum, Universitaetsstrasse 150, 44801 Bochum (Germany)

2010-11-15

The present work characterizes the microstructure of a hot-extruded Ti-45Al-5Nb-0.2B-0.2C (at.%) alloy with a fine-grained duplex microstructure after shear creep deformation (temperature 1023 K; shear stress 175 MPa; shear deformation 20%). Diffraction contrast transmission electron microscopy (TEM) was performed to identify ordinary dislocations, superdislocations and twins. The microstructure observed in TEM is interpreted taking into account the contribution of the applied stress and coherency stresses to the overall local stress state. Two specific locations in the lamellar part of the microstructure were analyzed, where either twins or superdislocations provided c-component deformation in the L1{sub 0} lattice of the {gamma} phase. Lamellar {gamma} grains can be in soft and hard orientations with respect to the resolved shear stress provided by the external load. The presence of twins can be rationalized by the superposition of the applied stress and local coherency stresses. The presence of superdislocations in hard {gamma} grains represents indirect evidence for additional contributions to the local stress state associated with stress redistribution during creep.

Improving the durability of the optical fiber sensor based on strain transfer analysis

Science.gov (United States)

Wang, Huaping; Jiang, Lizhong; Xiang, Ping

2018-05-01

To realize the reliable and long-term strain detection, the durability of optical fiber sensors has attracted more and more attention. The packaging technique has been considered as an effective method, which can enhance the survival ratios of optical fiber sensors to resist the harsh construction and service environment in civil engineering. To monitor the internal strain of structures, the embedded installation is adopted. Due to the different material properties between host material and the protective layer, the monitored structure embedded with sensors can be regarded as a typical model containing inclusions. Interfacial characteristic between the sensor and host material exists obviously, and the contacted interface is prone to debonding failure induced by the large interfacial shear stress. To recognize the local interfacial debonding damage and extend the effective life cycle of the embedded sensor, strain transfer analysis of a general three-layered sensing model is conducted to investigate the failure mechanism. The perturbation of the embedded sensor on the local strain field of host material is discussed. Based on the theoretical analysis, the distribution of the interfacial shear stress along the sensing length is characterized and adopted for the diagnosis of local interfacial debonding, and the sensitive parameters influencing the interfacial shear stress are also investigated. The research in this paper explores the interfacial debonding failure mechanism of embedded sensors based on the strain transfer analysis and provides theoretical basis for enhancing the interfacial bonding properties and improving the durability of embedded optical fiber sensors.

Micromechanics of soil responses in cyclic simple shear tests

Directory of Open Access Journals (Sweden)

Cui Liang

2017-01-01

Full Text Available Offshore wind turbine (OWT foundations are subjected to a combination of cyclic and dynamic loading arising from wind, wave, rotor and blade shadowing. Under cyclic loading, most soils change their characteristics including stiffness, which may cause the system natural frequency to approach the loading frequency and lead to unplanned resonance and system damage or even collapse. To investigate such changes and the underlying micromechanics, a series of cyclic simple shear tests were performed on the RedHill 110 sand with different shear strain amplitudes, vertical stresses and initial relative densities of soil. The test results showed that: (a Vertical accumulated strain is proportional to the shear strain amplitude but inversely proportional to relative density of soil; (b Shear modulus increases rapidly in the initial loading cycles and then the rate of increase diminishes and the shear modulus remains below an asymptote; (c Shear modulus increases with increasing vertical stress and relative density, but decreasing with increasing strain amplitude. Coupled DEM simulations were performed using PFC2D to analyse the micromechanics underlying the cyclic behaviour of soils. Micromechanical parameters (e.g. fabric tensor, coordination number were examined to explore the reasons for the various cyclic responses to different shear strain amplitudes or vertical stresses. Both coordination number and magnitude of fabric anisotropy contribute to the increasing shear modulus.

Rescaled Local Interaction Simulation Approach for Shear Wave Propagation Modelling in Magnetic Resonance Elastography

Directory of Open Access Journals (Sweden)

Z. Hashemiyan

2016-01-01

Full Text Available Properties of soft biological tissues are increasingly used in medical diagnosis to detect various abnormalities, for example, in liver fibrosis or breast tumors. It is well known that mechanical stiffness of human organs can be obtained from organ responses to shear stress waves through Magnetic Resonance Elastography. The Local Interaction Simulation Approach is proposed for effective modelling of shear wave propagation in soft tissues. The results are validated using experimental data from Magnetic Resonance Elastography. These results show the potential of the method for shear wave propagation modelling in soft tissues. The major advantage of the proposed approach is a significant reduction of computational effort.

Rescaled Local Interaction Simulation Approach for Shear Wave Propagation Modelling in Magnetic Resonance Elastography

Science.gov (United States)

Packo, P.; Staszewski, W. J.; Uhl, T.

2016-01-01

Properties of soft biological tissues are increasingly used in medical diagnosis to detect various abnormalities, for example, in liver fibrosis or breast tumors. It is well known that mechanical stiffness of human organs can be obtained from organ responses to shear stress waves through Magnetic Resonance Elastography. The Local Interaction Simulation Approach is proposed for effective modelling of shear wave propagation in soft tissues. The results are validated using experimental data from Magnetic Resonance Elastography. These results show the potential of the method for shear wave propagation modelling in soft tissues. The major advantage of the proposed approach is a significant reduction of computational effort. PMID:26884808

Effect of cohesion on local compaction and granulation of sheared soft granular materials

Directory of Open Access Journals (Sweden)

Roy Sudeshna

2017-01-01

Full Text Available This paper results from an ongoing investigation of the effect of cohesion on the compaction of sheared soft wet granular materials. We compare dry non-cohesive and wet moderately-to-strongly cohesive soft almost frictionless granular materials and report the effect of cohesion between the grains on the local volume fraction. We study this in a three dimensional, unconfined, slowly sheared split-bottom ring shear cell, where materials while sheared are subject to compression under the confining weight of the material above. Our results show that inter-particle cohesion has a considerable impact on the compaction of soft materials. Cohesion causes additional stresses, due to capillary forces between particles, leading to an increase in volume fraction due to higher compaction. This effect is not visible in a system of infinitely stiff particles. In addition, acting oppositely, we observe a general decrease in volume fraction due to increased cohesion for frictional particle, which we attribute to the role of contact friction that enhances dilation.

Analyzing shear band formation with high resolution X-ray diffraction

Energy Technology Data Exchange (ETDEWEB)

Pagan, Darren C.; Obstalecki, Mark; Park, Jun-Sang; Miller, Matthew P.

2018-04-01

Localization of crystallographic slip into shear bands during uniaxial compression of a copper single crystal is studied using very far-field high-energy diffraction microscopy (vff-HEDM). Diffracted intensity was collected in-situ as the crystal deformed using a unique mobile detector stage that provided access to multiple diffraction peaks with high-angular resolution. From the diffraction data, single crystal orientation pole figures (SCPFs) were generated and are used to track the evolution of the distribution of lattice orientation that develops as slip localizes. To aid the identification of 'signatures' of shear band formation and analyze the SCPF data, a model of slip-driven lattice reorientation within shear bands is introduced. Confidence is built in conclusions drawn from the SCPF data about the character of internal slip localization through comparisons with strain fields on the sample surface measured simultaneously using digital image correlation. From the diffraction data, we find that the active slip direction and slip plane are not directly aligned with the orientation of the shear bands that formed. In fact, by extracting the underlying slip system activity from the SCPF data, we show that intersecting shear bands measured on the surface of the sample arise from slip primarily on the same underlying single slip system. These new vff-HEDM results raise significant questions on the use of surface measurements for slip system activity estimation. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Structure-rheology relationship in a sheared lamellar fluid.

Science.gov (United States)

Jaju, S J; Kumaran, V

2016-03-01

The structure-rheology relationship in the shear alignment of a lamellar fluid is studied using a mesoscale model which provides access to the lamellar configurations and the rheology. Based on the equations and free energy functional, the complete set of dimensionless groups that characterize the system are the Reynolds number (ργL(2)/μ), the Schmidt number (μ/ρD), the Ericksen number (μγ/B), the interface sharpness parameter r, the ratio of the viscosities of the hydrophilic and hydrophobic parts μ(r), and the ratio of the system size and layer spacing (L/λ). Here, ρ and μ are the fluid density and average viscosity, γ is the applied strain rate, D is the coefficient of diffusion, B is the compression modulus, μ(r) is the maximum difference in the viscosity of the hydrophilic and hydrophobic parts divided by the average viscosity, and L is the system size in the cross-stream direction. The lattice Boltzmann method is used to solve the concentration and momentum equations for a two dimensional system of moderate size (L/λ=32) and for a low Reynolds number, and the other parameters are systematically varied to examine the qualitative features of the structure and viscosity evolution in different regimes. At low Schmidt numbers where mass diffusion is faster than momentum diffusion, there is fast local formation of randomly aligned domains with "grain boundaries," which are rotated by the shear flow to align along the extensional axis as time increases. This configuration offers a high resistance to flow, and the layers do not align in the flow direction even after 1000 strain units, resulting in a viscosity higher than that for an aligned lamellar phase. At high Schmidt numbers where momentum diffusion is fast, the shear flow disrupts layers before they are fully formed by diffusion, and alignment takes place by the breakage and reformation of layers by shear, resulting in defects (edge dislocations) embedded in a background of nearly aligned layers

Local Turbulence Suppression and Shear Flow Dynamics During qmin-Triggered Internal Transport Barriers on DIII-D

Science.gov (United States)

Shafer, M. W.; McKee, G. R.; Schlossberg, D. J.; Austin, M. E.; Burrell, K. H.

2008-11-01

Long-wavelength turbulence (kρiITBs) may form. Application of off-axis ECH slows the q-profile evolution and increases ρqmin, both of which enhance turbulence measurements using a new high-sensitivity large-area (8x,8) 2D BES array. The measured transient turbulence suppression is localized to the low-order rational surface (qmin= 2, 5/2, 3, etc.). Measured poloidal flow shear transiently exceeds the turbulence decorrelation rate, which is consistent with shear suppression. The localized suppression zone propagates radially outward, nearly coincident with the low-order surface.

The importance of Thermo-Hydro-Mechanical couplings and microstructure to strain localization in 3D continua with application to seismic faults. Part II: Numerical implementation and post-bifurcation analysis

Science.gov (United States)

Rattez, Hadrien; Stefanou, Ioannis; Sulem, Jean; Veveakis, Manolis; Poulet, Thomas

2018-06-01

In this paper we study the phenomenon of localization of deformation in fault gouges during seismic slip. This process is of key importance to understand frictional heating and energy budget during an earthquake. A infinite layer of fault gouge is modeled as a Cosserat continuum taking into account Thermo-Hydro-Mechanical (THM) couplings. The theoretical aspects of the problem are presented in the companion paper (Rattez et al., 2017a), together with a linear stability analysis to determine the conditions of localization and estimate the shear band thickness. In this Part II of the study, we investigate the post-bifurcation evolution of the system by integrating numerically the full system of non-linear equations using the method of Finite Elements. The problem is formulated in the framework of Cosserat theory. It enables to introduce information about the microstructure of the material in the constitutive equations and to regularize the mathematical problem in the post-localization regime. We emphasize the influence of the size of the microstructure and of the softening law on the material response and the strain localization process. The weakening effect of pore fluid thermal pressurization induced by shear heating is examined and quantified. It enhances the weakening process and contributes to the narrowing of shear band thickness. Moreover, due to THM couplings an apparent rate-dependency is observed, even for rate-independent material behavior. Finally, comparisons show that when the perturbed field of shear deformation dominates, the estimation of the shear band thickness obtained from linear stability analysis differs from the one obtained from the finite element computations, demonstrating the importance of post-localization numerical simulations.

Loading direction-dependent shear behavior at different temperatures of single-layer chiral graphene sheets

Science.gov (United States)

Zhao, Yang; Dong, Shuhong; Yu, Peishi; Zhao, Junhua

2018-06-01

The loading direction-dependent shear behavior of single-layer chiral graphene sheets at different temperatures is studied by molecular dynamics (MD) simulations. Our results show that the shear properties (such as shear stress-strain curves, buckling strains, and failure strains) of chiral graphene sheets strongly depend on the loading direction due to the structural asymmetry. The maximum values of both the critical buckling shear strain and the failure strain under positive shear deformation can be around 1.4 times higher than those under negative shear deformation. For a given chiral graphene sheet, both its failure strain and failure stress decrease with increasing temperature. In particular, the amplitude to wavelength ratio of wrinkles for different chiral graphene sheets under shear deformation using present MD simulations agrees well with that from the existing theory. These findings provide physical insights into the origins of the loading direction-dependent shear behavior of chiral graphene sheets and their potential applications in nanodevices.

Atomistic simulation study of the shear-band deformation mechanism in Mg-Cu metallic glasses

DEFF Research Database (Denmark)

Bailey, Nicholas; Schiøtz, Jakob; Jacobsen, Karsten Wedel

2006-01-01

We have simulated plastic deformation of a model Mg-Cu metallic glass in order to study shear banding. In uniaxial tension, we find a necking instability occurs rather than shear banding. We can force the latter to occur by deforming in plane strain, forbidding the change of length in one...... of the transverse directions. Furthermore, in most of the simulations a notch is used to initiate shear bands, which lie at a 45 degrees angle to the tensile loading direction. The shear bands are characterized by the Falk and Langer local measure of plastic deformation D-min(2), averaged here over volumes...... observe a slight decrease in density, up to 1%, within the shear band, which is consistent with notions of increased free volume or disorder within a plastically deforming amorphous material....

Assessment of homogeneity of the shear-strain pattern in Al–7 wt%Si casting alloy processed by high-pressure torsion

Energy Technology Data Exchange (ETDEWEB)

Cepeda-Jiménez, C.M., E-mail: carmen.cepeda@imdea.org [Department of Physical Metallurgy, CENIM, CSIC, Av. Gregorio del Amo 8, 28040 Madrid (Spain); Orozco-Caballero, A.; García-Infanta, J.M. [Department of Physical Metallurgy, CENIM, CSIC, Av. Gregorio del Amo 8, 28040 Madrid (Spain); Zhilyaev, A.P. [Institute for Metals Superplasticity Problems, Russian Academy of Science, 39 Khalturina, 450001 Ufa (Russian Federation); Ruano, O.A.; Carreño, F. [Department of Physical Metallurgy, CENIM, CSIC, Av. Gregorio del Amo 8, 28040 Madrid (Spain)

2014-03-01

An as-cast Al–7 wt%Si alloy was subjected to processing by high-pressure torsion (HPT) at room temperature, through 1/4, 1/2, 1 and 5 turns at a pressure of 6 GPa and two rotation speeds, 0.1 and 1 rpm. Vickers microhardness was measured along diameters of HPT disk surfaces. The final hardness values were higher than in the initial as-cast condition and, unexpectedly, nearly constant under all different processing conditions, and along the disk diameter. The microstructure was characterised by optical and scanning electron microscopy. The as-cast microstructure comprises equiaxed primary α dendrite cells embedded in the Al–Si eutectic constituent. The morphology and distribution of the eutectic constituent in the HPT processed materials is used to delineate the shear strain, which was analysed in the cross-section planes of the disks. A high degree of homogeneity in the imposed shear strain throughout the samples was observed, being congruent with the ideal rigid-body torsion. In addition, the high compressive pressure applied, causing compressive strain prior to the torsional strain, is responsible for the deformation-induced precipitation of small Si particles and for the (sub)grain refinement in the primary Al constituent. The role of torsional strain is that of increasing monothonically the redistribution of the eutectic silicon and the misorientation of the (sub)grains.

Effect of microstructure on the nucleation and initiation of adiabatic shear bands (ASBs) during impact

Energy Technology Data Exchange (ETDEWEB)

Boakye Yiadom, Solomon, E-mail: boakyeys@cc.umanitoba.ca; Khaliq Khan, Abdul, E-mail: abdulkhaliq.khan@umanitoba.ca; Bassim, Nabil, E-mail: nabil.bassim@ad.umanitoba.ca

2014-10-06

While instability may occur homogenously during plastic deformation, the formation of adiabatic shear band (ASBs) does not follow a homogenous instability during impact. Geometrical stress concentration sites and/or microstructural inhomogeneities result in the nucleation and initiation of shear strain localization. In this study, initial microstructural inhomogeneity was found to produce nucleation sites for the initiation of ASBs. It was observed that double misfit interfaces and boundary layers with random arrangement of atomic columns are formed around precipitated carbides and they increase the volume fraction of dislocation sources within the specimens. The AISI 4340 steel specimens which were tempered at the lowest temperature had smaller precipitated carbides with high aspect ratios densely distributed within the matrix and were easily susceptible to the formation of ASBs. As the tempering temperature increased, the relative sizes of the carbides increased with a corresponding reduction in their aspect ratios and their distribution density within the matrix and thus were more resistant to the formation of ASBs. In this study, it is demonstrated that the intersection of an activated dislocation source with the direction of maximum shear (regions of stress concentrations) within the specimens during impact, is a necessary condition for the point of intersection to act as a possible site for the nucleation of ASBs, depending on the rate of dislocation generation, local strain and strain rate. At a constant carbide volume fraction, the higher susceptibility of the tempered specimens to the initiation of ASBs is attributed to the volume fraction of the points of intersection between activated dislocation sources and direction of maximum shear during impact. Additionally, the smaller carbides, with their higher aspect ratios and distribution densities, accentuate the effect of strain gradients and the microstructural inhomogeneities associated with the tempered

Evaluation of healthy muscle tissue by strain and shear wave elastography – Dependency on depth and ROI position in relation to underlying bone

DEFF Research Database (Denmark)

Ewertsen, Caroline; Carlsen, Jonathan Frederik; Christiansen, Iben Riishede

2016-01-01

and methods: Ten healthy volunteers (five males and five females) had their biceps brachii, gastrocnemius, and quadriceps muscle examined with strain- and shear wave elastography at three different depths and in regions located above bone and beside bone. Strain ratios were averaged from cine-loops of 10 s...

Adiabatic shear behaviors in rolled and annealed pure titanium subjected to dynamic impact loading

Energy Technology Data Exchange (ETDEWEB)

Kuang, Lianjun; Chen, Zhiyong, E-mail: czysh@netease.com; Jiang, Yanghui; Wang, Zhiming; Wang, Renke; Liu, Chuming

2017-02-08

The hat-shaped samples cut from rolled and annealed titanium plates were prepared to explore the adiabatic shear behaviors subjected to high-strain-rate deformation operated via Split Hopkinson Pressure Bar. The dynamic shear response calculation reveals that dynamic deformation processes of both state samples can be divided in similar three stages but rolled sample shows a higher susceptibility of adiabatic shear localization compared with the annealed one. Optical microscopy and electronic backscatter diffraction technique (EBSD) were used to systematically analyze the microstructure and texture characteristics. The results show that adiabatic shear bands form in both state samples and rotational dynamic recrystallization (RDRX) occurs within shear area and results in the formation of ultrafine equiaxed grains. Furthermore, ultrafine equiaxed grains within adiabatic shear bands have the same texture feature that <11–20> direction and {10-10} plane parallel to macro local shear direction and shear plane respectively. In the deformation region around the shear band, {10–12} <–1011> tensile and {11–22} <11-2-3> compressive two types twins are observed in both state samples and {10–12} <–1011> tensile twins are more frequently observed in rolled sample. In the rolled sample, {10–12} <–1011> tensile twins are more likely to happen in the hat-brim side than the hat-body side due to the difference of stress state in two sides.

Simulation of strain localization in polycrystals

International Nuclear Information System (INIS)

Deryugin, Ye.Ye.; Payuk, V.A.; Lasko, G.V.

2002-01-01

In the work simulation of plastic deformation evolution is presented for the case of polycrystals under external loading. Strain localization in polycrystal is simulated analytically following an unconventional method. The model is based on new progressive relaxation elements methods. Emphasis of the model is combining of discrete methods and continual approach. It makes possible to present local sites of plastic deformation analytically in a continuous medium and to calculate their respective no uniform stress field

Experiments on sheet metal shearing

OpenAIRE

Gustafsson, Emil

2013-01-01

Within the sheet metal industry, different shear cutting technologies are commonly used in several processing steps, e.g. in cut to length lines, slitting lines, end cropping etc. Shearing has speed and cost advantages over competing cutting methods like laser and plasma cutting, but involves large forces on the equipment and large strains in the sheet material.Numerical models to predict forces and sheared edge geometry for different sheet metal grades and different shear parameter set-ups a...

Quantifying the Variation in Shear Zone Character with Depth: a Case Study from the Simplon Shear Zone, Central Alps

Science.gov (United States)

Cawood, T. K.; Platt, J. P.

2017-12-01

A widely-accepted model for the rheology of crustal-scale shear zones states that they comprise distributed strain at depth, in wide, high-temperature shear zones, which narrow to more localized, high-strain zones at lower temperature and shallower crustal levels. We test and quantify this model by investigating how the width, stress, temperature and deformation mechanisms change with depth in the Simplon Shear Zone (SSZ). The SSZ marks a major tectonic boundary in the central Alps, where normal-sense motion and rapid exhumation of the footwall have preserved evidence of older, deeper deformation in rocks progressively further into the currently-exposed footwall. As such, microstructures further from the brittle fault (which represents the most localized, most recently-active part of the SSZ) represent earlier, higher- temperature deformation from deeper crustal levels, while rocks closer to the fault have been overprinted by successively later, cooler deformation at shallower depths. This study uses field mapping and microstructural studies to identify zones representing deformation at various crustal levels, and characterize each in terms of zone width (representing width of the shear zone at that time and depth) and dominant deformation mechanism. In addition, quartz- (by Electron Backscatter Diffraction, EBSD) and feldspar grain size (measured optically) piezometry are used to calculate the flow stress for each zone, while the Ti-in-quartz thermometer (TitaniQ) is used to calculate the corresponding temperature of deformation. We document the presence of a broad zone in which quartz is recrystallized by the Grain Boundary Migration (GBM) mechanism and feldspar by Subgrain Rotation (SGR), which represents the broad, deep zone of deformation occurring at relatively high temperatures and low stresses. In map view, this transitions to successively narrower zones, respectively characterized by quartz SGR and feldspar Bulge Nucleation (BLG); quartz BLG and brittle

Local stress modification during in situ transmission electron microscopy straining experiments

Czech Academy of Sciences Publication Activity Database

Zárubová, Niva; Gemperle, Antonín; Gemperlová, Juliana

2007-01-01

Roč. 462, - (2007), s. 407-411 ISSN 0921-5093 R&D Projects: GA ČR GA202/04/2016 Institutional research plan: CEZ:AV0Z10100520 Keywords : in situ TEM straining, Local stress in a strained foil * local stress in a strained foil Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.457, year: 2007

Response of single polymers to localized step strains

NARCIS (Netherlands)

Panja, D.

2009-01-01

In this paper, the response of single three-dimensional phantom and self-avoiding polymers to localized step strains are studied for two cases in the absence of hydrodynamic interactions: (i) Polymers tethered at one end with the strain created at the point of tether, and (ii) free polymers with the

Heat transfer modeling in asymmetrical sheet rolling of aluminium alloys with ultra high shear strain

Directory of Open Access Journals (Sweden)

Pesin Alexander

2016-01-01

Full Text Available Asymmetrical sheet rolling is a method of severe plastic deformation (SPD for production of aluminium alloys with UFG structure. Prediction of sheet temperature during SPD is important. The temperature of sheet is changed due to the conversion of mechanical work into heat through sliding on contact surfaces and high shear strain. Paper presents the results of FEM simulation of the effect of contact friction, rolling speed and rolls speed ratio on the heating of aluminium sheets during asymmetrical rolling.

Study on reinforced lightweight coconut shell concrete beam behavior under shear

International Nuclear Information System (INIS)

Gunasekaran, K.; Annadurai, R.; Kumar, P.S.

2013-01-01

Highlights: • Coconut shell used as aggregate in concrete production. • Coconut shell concrete beam behavior studied under shear. • Coconut shell concrete beam behavior are compared with control concrete beams. - Abstract: Lightweight concrete has been produced using crushed coconut shell as coarse aggregate. The shear behavior of reinforced concrete beam made with coconut shell is analyzed and compared with the normal control concrete. Eight beams, four with coconut shell concrete and four with normal control concrete were fabricated and tested. Study includes the structural shear behavior, shear capacity, cracking behavior, deflection behavior, ductility, strains in concrete and in reinforcement. It was observed that the shear behavior of coconut shell concrete is comparable to that of other lightweight concretes. The results of concrete compression strain and steel tension strain showed that coconut shell concrete is able to achieve its full strain capacity under shear loadings. However, the failure zones of coconut shell concrete were larger than for control concrete beams

Stress-strain relation of bentonite at undrained shear. Laboratory tests to investigate the influence of material composition and test technique

Energy Technology Data Exchange (ETDEWEB)

Dueck, Ann; Boergesson, Lennart; Johannesson, Lars-Erik (Clay Technology AB, Lund (Sweden))

2010-12-15

This report describes a laboratory study conducted to update the material model of the buffer material used in the analyses of the effect of a rock shear through a deposition hole. The study considers some new conditions and is especially focused on the reference case with MX-80Ca developed for SR-Site (MX-80 ion exchanged to Ca). The material model is based on relations between density, swelling pressure, shear strength and rate of strain. The reference model is described by Boergesson et al. (2010). The laboratory study is focused on undrained stress-strain-strength properties, which have been studied mainly by conducting triaxial tests and unconfined compression tests. The test results are compared to the earlier measurements and models which show that the new results fit very well into the general picture and models. For the new conditions suitable values of constants included in the model are proposed

Stress-strain relation of bentonite at undrained shear. Laboratory tests to investigate the influence of material composition and test technique

International Nuclear Information System (INIS)

Dueck, Ann; Boergesson, Lennart; Johannesson, Lars-Erik

2010-12-01

This report describes a laboratory study conducted to update the material model of the buffer material used in the analyses of the effect of a rock shear through a deposition hole. The study considers some new conditions and is especially focused on the reference case with MX-80Ca developed for SR-Site (MX-80 ion exchanged to Ca). The material model is based on relations between density, swelling pressure, shear strength and rate of strain. The reference model is described by Boergesson et al. (2010). The laboratory study is focused on undrained stress-strain-strength properties, which have been studied mainly by conducting triaxial tests and unconfined compression tests. The test results are compared to the earlier measurements and models which show that the new results fit very well into the general picture and models. For the new conditions suitable values of constants included in the model are proposed

Microstructure evolution of pure copper during a single pass of simple shear extrusion (SSE): role of shear reversal

Energy Technology Data Exchange (ETDEWEB)

Bagherpour, E., E-mail: e.bagherpour@semnan.ac.ir [Faculty of Metallurgical and Materials Engineering, Semnan University, Semnan (Iran, Islamic Republic of); Department of Mechanical Engineering, Doshisha University, Kyotanabe, Kyoto 610–0394 (Japan); Qods, F., E-mail: qods@semnan.ac.ir [Faculty of Metallurgical and Materials Engineering, Semnan University, Semnan (Iran, Islamic Republic of); Ebrahimi, R., E-mail: ebrahimy@shirazu.ac.ir [Department of Materials Science and Engineering, School of Engineering, Shiraz University, Shiraz (Iran, Islamic Republic of); Miyamoto, H., E-mail: hmiyamot@mail.doshisha.ac.jp [Department of Mechanical Engineering, Doshisha University, Kyotanabe, Kyoto 610–0394 (Japan)

2016-06-01

In the present paper the role of shear reversal on microstructure, texture and mechanical properties of pure copper during a single pass of the simple shear extrusion (SSE) process was investigated. For SSE processing an appropriate die with a linear die profile was designed and constructed, which imposes forward shear in the first half and reverse shear in the second half channels. Electron back-scattering diffraction (EBSD), transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) were used to evaluate the microstructure of the deformed samples. The geometrical nature of this process imposes a distribution of strain results in the inhomogeneous microstructure and the hardness throughout the plane perpendicular to the extrusion direction. Strain reversal during the process results in a slight reduction in dislocation density, the hardness and mean disorientation angle of the samples, and an increase in the grain size. After a complete pass of SSE, dislocation density decreased by ~14% if compared to the middle of the process. This suggests that the dislocation annihilation occurred by the reversal of the shear strain. The simple shear textures were formed gradually and the strongest simple shear textures were observed on the middle of the SSE channel. The degree of the simple shear textures decreases with the distance from the middle plane where the shear is reversed, but the simple shear textures are still the major components after exit of the channel. Hardness variation was modeled by contributions from dislocation strengthening and grain boundary strengthening, where dislocation density is approximated by the misorientation angle of LAGBs which are regarded as dislocation cell boundaries. As a result, the hardness can be predicted successfully by the microstructural features, i.e. the low-angle boundaries, the mean misorientation angle and the fraction of high-angle grain boundaries.

Structural state diagram of concentrated suspensions of jammed soft particles in oscillatory shear flow

Science.gov (United States)

Khabaz, Fardin; Cloitre, Michel; Bonnecaze, Roger T.

2018-03-01

In a recent study [Khabaz et al., Phys. Rev. Fluids 2, 093301 (2017), 10.1103/PhysRevFluids.2.093301], we showed that jammed soft particle glasses (SPGs) crystallize and order in steady shear flow. Here we investigate the rheology and microstructures of these suspensions in oscillatory shear flow using particle-dynamics simulations. The microstructures in both types of flows are similar, but their evolutions are very different. In both cases the monodisperse and polydisperse suspensions form crystalline and layered structures, respectively, at high shear rates. The crystals obtained in the oscillatory shear flow show fewer defects compared to those in the steady shear. SPGs remain glassy for maximum oscillatory strains less than about the yield strain of the material. For maximum strains greater than the yield strain, microstructural and rheological transitions occur for SPGs. Polydisperse SPGs rearrange into a layered structure parallel to the flow-vorticity plane for sufficiently high maximum shear rates and maximum strains about 10 times greater than the yield strain. Monodisperse suspensions form a face-centered cubic (FCC) structure when the maximum shear rate is low and hexagonal close-packed (HCP) structure when the maximum shear rate is high. In steady shear, the transition from a glassy state to a layered one for polydisperse suspensions included a significant induction strain before the transformation. In oscillatory shear, the transformation begins to occur immediately and with different microstructural changes. A state diagram for suspensions in large amplitude oscillatory shear flow is found to be in close but not exact agreement with the state diagram for steady shear flow. For more modest amplitudes of around one to five times the yield strain, there is a transition from a glassy structure to FCC and HCP crystals, at low and high frequencies, respectively, for monodisperse suspensions. At moderate frequencies, the transition is from glassy to HCP via

Experimental Investigation of Adiabatic Shear Banding at Different Impact Velocities

Science.gov (United States)

1993-01-01

plasticity and ASB’s is the Double-notch Shear specimen, it has been decided to use this concept in shear testing at medium and high strain rates...is the Double-notch Shear specimen. it has been decided to use this concept in shear testing at medium and high strain rates. Originally, Campbell...7] C. Fressengeas, Analyse dynamique 61asto-viscoplastique de l’h6tdrogdndit6 de la ddforma- tion plastique de cisalllement, Proc. Int. Conf. on

Analysis of heterogeneities in strain and microstructure in aluminum alloy and magnesium processed by high-pressure torsion

Energy Technology Data Exchange (ETDEWEB)

Panda, Subrata, E-mail: subrata.panda@univ-lorraine.fr [Université de Lorraine, Laboratory of Excellence on Design of Alloy Metals for low-mass Structures (DAMAS), Ile du Saulcy, Metz F-57045 (France); Université de Lorraine, Laboratoire d' Etude des Microstructures et de Mécanique des Matériaux (LEM3 UMR 7239), Ile du Saulcy, Metz F-57045 (France); Toth, Laszlo S., E-mail: laszlo.toth@univ-lorraine.fr [Université de Lorraine, Laboratory of Excellence on Design of Alloy Metals for low-mass Structures (DAMAS), Ile du Saulcy, Metz F-57045 (France); Université de Lorraine, Laboratoire d' Etude des Microstructures et de Mécanique des Matériaux (LEM3 UMR 7239), Ile du Saulcy, Metz F-57045 (France); Fundenberger, Jean-Jacques, E-mail: jean-jacques.fundenberger@univ-lorraine.fr [Université de Lorraine, Laboratory of Excellence on Design of Alloy Metals for low-mass Structures (DAMAS), Ile du Saulcy, Metz F-57045 (France); Université de Lorraine, Laboratoire d' Etude des Microstructures et de Mécanique des Matériaux (LEM3 UMR 7239), Ile du Saulcy, Metz F-57045 (France); Perroud, Olivier, E-mail: olivier.perroud@univ-lorraine.fr [Université de Lorraine, Laboratory of Excellence on Design of Alloy Metals for low-mass Structures (DAMAS), Ile du Saulcy, Metz F-57045 (France); Université de Lorraine, Laboratoire d' Etude des Microstructures et de Mécanique des Matériaux (LEM3 UMR 7239), Ile du Saulcy, Metz F-57045 (France); and others

2017-01-15

Two distinct bulk light metals were opted to study the shear strain evolution and associated heterogeneities in texture/microstructure development during torsional straining by high pressure torsion (HPT): a face centered cubic Al alloy (A5086) and a hexagonal commercial purity Mg. Relatively thick disk samples - four times thicker than usually employed in HPT process - were processed to 180° and 270° rotations. With the help of X-ray tomography, the shear strain gradients were examined in the axial direction. The results showed strongly localized shear deformation in the middle plane of the disks in both materials. These gradients involved strong heterogeneities in texture, microstructure and associated hardness, in particular through the thickness direction at the periphery of the disk where the interplay between significant strain hardening and possible dynamic recrystallization could occur. - Highlights: •HPT processing was conducted on bulk specimens thicker than the usual thin-disks. •The Al alloy (A5086) and commercial purity magnesium samples were compared. •Distributions of strain and microhardness were evaluated in the radial and axial direction. •Plastic deformation is highly localized in the middle plane at outer edge in both materials. •Different DRX rates governed the differences in microstructure and hardening behavior.

Thermal conductivity of graphene nanoribbons under shear deformation: A molecular dynamics simulation

Science.gov (United States)

Zhang, Chao; Hao, Xiao-Li; Wang, Cui-Xia; Wei, Ning; Rabczuk, Timon

2017-01-01

Tensile strain and compress strain can greatly affect the thermal conductivity of graphene nanoribbons (GNRs). However, the effect of GNRs under shear strain, which is also one of the main strain effect, has not been studied systematically yet. In this work, we employ reverse nonequilibrium molecular dynamics (RNEMD) to the systematical study of the thermal conductivity of GNRs (with model size of 4 nm × 15 nm) under the shear strain. Our studies show that the thermal conductivity of GNRs is not sensitive to the shear strain, and the thermal conductivity decreases only 12–16% before the pristine structure is broken. Furthermore, the phonon frequency and the change of the micro-structure of GNRs, such as band angel and bond length, are analyzed to explore the tendency of thermal conductivity. The results show that the main influence of shear strain is on the in-plane phonon density of states (PDOS), whose G band (higher frequency peaks) moved to the low frequency, thus the thermal conductivity is decreased. The unique thermal properties of GNRs under shear strains suggest their great potentials for graphene nanodevices and great potentials in the thermal managements and thermoelectric applications. PMID:28120921

Earthquake induced rock shear through a deposition hole. Influence of shear plane inclination and location as well as buffer properties on the damage caused to the canister

International Nuclear Information System (INIS)

Boergesson, Lennart; Hernelind, Jan

2006-10-01

The effect on the canister of an earthquake induced 20 cm rock shear with the shear rate 1 m/s along a fracture intersecting a deposition hole in a KBS-V repository has been investigated for a number of different shear cases and for different properties of the buffer material. The scenarios have been modelled with the finite element method and calculations have been done using the code ABAQUS. D-element models of the rock, the buffer and the canister have been used. Contact elements that can model separation have been used for the interfaces between the buffer and the rock and the interfaces between the buffer and the canister. The influence of mainly the following factors has been investigated: 1. Inclination of the intersecting fracture. 2. Shear direction when the fracture is not horizontal (inclination deviates from 90 deg). 3. Location of the shear plane when the inclination is 90 deg. 4. Magnitude of the shear displacement. 5. Bentonite type. 6. Bentonite density. 7. Transformation of the buffer to illite or cemented bentonite. The results from the calculations show that all these factors have important influence on the damage of the canister but the influence is for most factors not easily described since there are mutual interferences between the different factors. Plastic strain larger than 1% was reached in the copper already at 10 cm shear in all cases with Na- and Ca- bentonite. However, for several cases of Na-bentonite and one case of Ca-bentonite such plastic strain was only reached in the lid. The plastic strain in the steel was generally smaller than in the copper mainly due to the higher yield stress in the steel. For all cases of Na-bentonite except one and for about half of the Ca-bentonite cases the plastic strain in the steel was smaller than 1% after 10 cm shear. The shear inclination 45 deg was more harmful for the copper tube than the shear inclination 90 deg when tension shear was considered. At the shear inclinations 45 deg and 22.5 deg

Earthquake induced rock shear through a deposition hole. Influence of shear plane inclination and location as well as buffer properties on the damage caused to the canister

Energy Technology Data Exchange (ETDEWEB)

Boergesson, Lennart [Clay Technology AB, Lund (Sweden); Hernelind, Jan [5T Engineering AB, Vaesteraas (Sweden)

2006-10-15

The effect on the canister of an earthquake induced 20 cm rock shear with the shear rate 1 m/s along a fracture intersecting a deposition hole in a KBS-V repository has been investigated for a number of different shear cases and for different properties of the buffer material. The scenarios have been modelled with the finite element method and calculations have been done using the code ABAQUS. D-element models of the rock, the buffer and the canister have been used. Contact elements that can model separation have been used for the interfaces between the buffer and the rock and the interfaces between the buffer and the canister. The influence of mainly the following factors has been investigated: 1. Inclination of the intersecting fracture. 2. Shear direction when the fracture is not horizontal (inclination deviates from 90 deg). 3. Location of the shear plane when the inclination is 90 deg. 4. Magnitude of the shear displacement. 5. Bentonite type. 6. Bentonite density. 7. Transformation of the buffer to illite or cemented bentonite. The results from the calculations show that all these factors have important influence on the damage of the canister but the influence is for most factors not easily described since there are mutual interferences between the different factors. Plastic strain larger than 1% was reached in the copper already at 10 cm shear in all cases with Na- and Ca- bentonite. However, for several cases of Na-bentonite and one case of Ca-bentonite such plastic strain was only reached in the lid. The plastic strain in the steel was generally smaller than in the copper mainly due to the higher yield stress in the steel. For all cases of Na-bentonite except one and for about half of the Ca-bentonite cases the plastic strain in the steel was smaller than 1% after 10 cm shear. The shear inclination 45 deg was more harmful for the copper tube than the shear inclination 90 deg when tension shear was considered. At the shear inclinations 45 deg and 22.5 deg

The dynamics of a shear band

Science.gov (United States)

Giarola, Diana; Capuani, Domenico; Bigoni, Davide

2018-03-01

A shear band of finite length, formed inside a ductile material at a certain stage of a continued homogeneous strain, provides a dynamic perturbation to an incident wave field, which strongly influences the dynamics of the material and affects its path to failure. The investigation of this perturbation is presented for a ductile metal, with reference to the incremental mechanics of a material obeying the J2-deformation theory of plasticity (a special form of prestressed, elastic, anisotropic, and incompressible solid). The treatment originates from the derivation of integral representations relating the incremental mechanical fields at every point of the medium to the incremental displacement jump across the shear band faces, generated by an impinging wave. The boundary integral equations (under the plane strain assumption) are numerically approached through a collocation technique, which keeps into account the singularity at the shear band tips and permits the analysis of an incident wave impinging a shear band. It is shown that the presence of the shear band induces a resonance, visible in the incremental displacement field and in the stress intensity factor at the shear band tips, which promotes shear band growth. Moreover, the waves scattered by the shear band are shown to generate a fine texture of vibrations, parallel to the shear band line and propagating at a long distance from it, but leaving a sort of conical shadow zone, which emanates from the tips of the shear band.

Localized strain measurements of the intervertebral disc annulus during biaxial tensile testing.

Science.gov (United States)

Karakolis, Thomas; Callaghan, Jack P

2015-01-01

Both inter-lamellar and intra-lamellar failures of the annulus have been described as potential modes of disc herniation. Attempts to characterize initial lamellar failure of the annulus have involved tensile testing of small tissue samples. The purpose of this study was to evaluate a method of measuring local surface strains through image analysis of a tensile test conducted on an isolated sample of annular tissue in order to enhance future studies of intervertebral disc failure. An annulus tissue sample was biaxial strained to 10%. High-resolution images captured the tissue surface throughout testing. Three test conditions were evaluated: submerged, non-submerged and marker. Surface strains were calculated for the two non-marker conditions based on motion of virtual tracking points. Tracking algorithm parameters (grid resolution and template size) were varied to determine the effect on estimated strains. Accuracy of point tracking was assessed through a comparison of the non-marker conditions to a condition involving markers placed on tissue surface. Grid resolution had a larger effect on local strain than template size. Average local strain error ranged from 3% to 9.25% and 0.1% to 2.0%, for the non-submerged and submerged conditions, respectively. Local strain estimation has a relatively high potential for error. Submerging the tissue provided superior strain estimates.

The effects of buoyancy on shear-induced melt bands in a compacting porous medium

Science.gov (United States)

Butler, S. L.

2009-03-01

It has recently been shown [Holtzman, B., Groebner, N., Zimmerman, M., Ginsberg, S., Kohlstedt, D., 2003. Stress-driven melt segregation in partially molten rocks. Geochem. Geophys. Geosyst. 4, Art. No. 8607; Holtzman, B.K., Kohlstedt, D.L., 2007. Stress-driven melt segregation and strain partitioning in partially molten rocks: effects of stress and strain. J. Petrol. 48, 2379-2406] that when partially molten rock is subjected to simple shear, bands of high and low porosity are formed at a particular angle to the direction of instantaneous maximum extension. These have been modeled numerically and it has been speculated that high porosity bands may form an interconnected network with a bulk, effective permeability that is enhanced in a direction parallel to the bands. As a result, the bands may act to focus mantle melt towards the axis of mid-ocean ridges [Katz, R.F., Spiegelman, M., Holtzman, B., 2006. The dynamics of melt and shear localization in partially molten aggregates. Nature 442, 676-679]. In this contribution, we examine the combined effects of buoyancy and matrix shear on a deforming porous layer. The linear theory of Spiegelman [Spiegelman, M., 1993. Flow in deformable porous media. Part 1. Simple analysis. J. Fluid Mech. 247, 17-38; Spiegelman, M., 2003. Linear analysis of melt band formation by simple shear. Geochem. Geophys. Geosyst. 4, doi:10.1029/2002GC000499, Article 8615] and Katz et al. [Katz, R.F., Spiegelman, M., Holtzman, B., 2006. The dynamics of melt and shear localization in partially molten aggregates. Nature 442, 676-679] is generalized to include both the effects of buoyancy and matrix shear on a deformable porous layer with strain-rate dependent rheology. The predictions of linear theory are compared with the early time evolution of our 2D numerical model and they are found to be in excellent agreement. For conditions similar to the upper mantle, buoyancy forces can be similar to or much greater than matrix shear-induced forces. The

Measurement of earthquake-induced shear strain in sandy gravel

International Nuclear Information System (INIS)

Ohkawa, I.; Futaki, M.; Yamanouchi, H.

1989-01-01

The nuclear power reactor buildings have been constructed on the hard rock ground formed in or before the Tertiary in Japan. This is mainly because the nuclear reactor building is much heavier than the common buildings and requires a large bearing capacity of the underlying soil deposit, and additionally the excessive deformation in soil deposit might cause damage in reactor building and subsequently cause the malfunction of the internal important facilities. Another reason is that the Quaternary soil deposit is not fully known with respect to its dynamic property. The gravel, and the sandy gravel, the representative soils of the Quaternary, have been believed to be suitable soil deposits to support the foundation of a common building, although the soils have rarely been investigated so closely on their physical properties quantitatively. In this paper, the dynamic deformability, i.e., the shear stress-strain relationship of the Quaternary diluvial soil deposit is examined through the earthquake ground motion measurement using accelerometers, pore-pressure meters, the specific devices developed in this research work. The objective soil deposit in this research is the sandy gravel of the diluvial and the alluvial

Local particle flux reversal under strongly sheared flow

International Nuclear Information System (INIS)

Terry, P.W.; Newman, D.E.; Ware, A.S.

2003-01-01

The advection of electron density by turbulent ExB flow with linearly varying mean yields a particle flux that can reverse sign at certain locations along the direction of magnetic shear. The effect, calculated for strong flow shear, resides in the density-potential cross phase. It is produced by the interplay between the inhomogeneities of magnetic shear and flow shear, but subject to a variety of conditions and constraints. The regions of reversed flux tend to wash out if the turbulence consists of closely spaced modes of different helicities, but survive if modes of a single helicity are relatively isolated. The reversed flux becomes negligible if the electron density response is governed by electron scales while the eigenmode is governed by ion scales. The relationship of these results to experimentally observe flux reversals is discussed

Noninvasive characterization of carotid plaque strain.

Science.gov (United States)

Khan, Amir A; Sikdar, Siddhartha; Hatsukami, Thomas; Cebral, Juan; Jones, Michael; Huston, John; Howard, George; Lal, Brajesh K

2017-06-01

Current risk stratification of internal carotid artery plaques based on diameter-reducing percentage stenosis may be unreliable because ischemic stroke results from plaque disruption with atheroembolization. Biomechanical forces acting on the plaque may render it vulnerable to rupture. The feasibility of ultrasound-based quantification of plaque displacement and strain induced by hemodynamic forces and their relationship to high-risk plaques have not been determined. We studied the feasibility and reliability of carotid plaque strain measurement from clinical B-mode ultrasound images and the relationship of strain to high-risk plaque morphology. We analyzed carotid ultrasound B-mode cine loops obtained in patients with asymptomatic ≥50% stenosis during routine clinical scanning. Optical flow methods were used to quantify plaque motion and shear strain during the cardiac cycle. The magnitude (maximum absolute shear strain rate [MASSR]) and variability (entropy of shear strain rate [ESSR] and variance of shear strain rate [VSSR]) of strain were combined into a composite shear strain index (SSI), which was assessed for interscan repeatability and correlated with plaque echolucency. Nineteen patients (mean age, 70 years) constituting 36 plaques underwent imaging; 37% of patients (n = 7) showed high strain (SSI ≥0.5; MASSR, 2.2; ESSR, 39.7; VSSR, 0.03) in their plaques; the remaining clustered into a low-strain group (SSI routine B-mode imaging using clinical ultrasound machines. High plaque strain correlates with known high-risk echolucent morphology. Strain measurement can complement identification of patients at high risk for plaque disruption and stroke. Copyright © 2017 Society for Vascular Surgery. Published by Elsevier Inc. All rights reserved.

The response of dense dry granular material to the shear reversal

Science.gov (United States)

Zhang, Jie; Ren, Jie; Farhadi, Somayeh; Behringer, Robert

2008-11-01

We have performed two dimensional granular experiments under pure shear using bidisperse photo-elastic disks. Starting from a stress free state, a square box filled with granular particles is subject to shear. The forward shears involved various number of steps, leading to maximum strains between 0.1 and 0.3. The area is kept constant during the shear. The network of force chains gradually built up as the strain increased, leading to increased pressure and shear stress. Reverse shear was then applied to the system. Depending on the initial packing fraction and the strain at which the shear is reversed, the force chain network built prior to the shear reversal may be destroyed completely or partially destroyed. Following the force chain weakening, when the reserve shear is continuously applied to the system, there is a force chain strengthening. Following each change of the system, contact forces of individual disks were measured by applying an inverse algorithm. We also kept track of the displacement and angle of rotation of every particle from frame to frame. We present the results for the structure failure and reconstruction during shear reversals. We also present data for stresses, contact force distributions and other statistical measures.

Local transport barrier formation and relaxation in reverse-shear plasmas on the TFTR tokamak

International Nuclear Information System (INIS)

Synakowski, E.J.; Beer, M.A.

1997-02-01

The roles of turbulence stabilization by sheared E x B flow and Shafranov-shift gradients are examined for TFTR. Enhanced Reverse-Shear plasmas. Both effects in combination provide the basis of a positive-feedback model that predicts reinforced turbulence suppression with increasing pressure gradient. Local fluctuation behavior at the onset of ERS confinement is consistent with this framework. The power required for transitions into the ERS regime are lower when high power neutral beams are applied earlier in the current profile evolution, consistent with the suggestion that both effects play a role. Separation of the roles of E x B and Shafranov shift effects was performed by varying the E x B shear through changes in the toroidal velocity with nearly-steady-state pressure profiles. Transport and fluctuation levels increase only when E x B shearing rates are driven below a critical value that is comparable to the fastest linear growth rates of the dominant instabilities. While a turbulence suppression criterion that involves the ratio of shearing to linear growth rates is in accord with many of these results, the existence of hidden dependencies of the criterion is suggested in experiments where the toroidal field was varied. The forward transition into the ERS regime has also been examined in strongly rotating plasmas. The power threshold is higher with unidirectional injection than with balanced injection

Beam model for seismic analysis of complex shear wall structure based on the strain energy equivalence

International Nuclear Information System (INIS)

Reddy, G.R.; Mahajan, S.C.; Suzuki, Kohei

1997-01-01

A nuclear reactor building structure consists of shear walls with complex geometry, beams and columns. The complexity of the structure is explained in the section Introduction. Seismic analysis of the complex reactor building structure using the continuum mechanics approach may produce good results but this method is very difficult to apply. Hence, the finite element approach is found to be an useful technique for solving the dynamic equations of the reactor building structure. In this approach, the model which uses finite elements such as brick, plate and shell elements may produce accurate results. However, this model also poses some difficulties which are explained in the section Modeling Techniques. Therefore, seismic analysis of complex structures is generally carried out using a lumped mass beam model. This model is preferred because of its simplicity and economy. Nevertheless, mathematical modeling of a shear wall structure as a beam requires specialized skill and a thorough understanding of the structure. For accurate seismic analysis, it is necessary to model more realistically the stiffness, mass and damping. In linear seismic analysis, modeling of the mass and damping may pose few problems compared to modeling the stiffness. When used to represent a complex structure, the stiffness of the beam is directly related to the shear wall section properties such as area, shear area and moment of inertia. Various beam models which are classified based on the method of stiffness evaluation are also explained under the section Modeling Techniques. In the section Case Studies the accuracy and simplicity of the beam models are explained. Among various beam models, the one which evaluates the stiffness using strain energy equivalence proves to be the simplest and most accurate method for modeling the complex shear wall structure. (author)

FEM × DEM: a new efficient multi-scale approach for geotechnical problems with strain localization

Directory of Open Access Journals (Sweden)

Nguyen Trung Kien

2017-01-01

Full Text Available The paper presents a multi-scale modeling of Boundary Value Problem (BVP approach involving cohesive-frictional granular materials in the FEM × DEM multi-scale framework. On the DEM side, a 3D model is defined based on the interactions of spherical particles. This DEM model is built through a numerical homogenization process applied to a Volume Element (VE. It is then paired with a Finite Element code. Using this numerical tool that combines two scales within the same framework, we conducted simulations of biaxial and pressuremeter tests on a cohesive-frictional granular medium. In these cases, it is known that strain localization does occur at the macroscopic level, but since FEMs suffer from severe mesh dependency as soon as shear band starts to develop, the second gradient regularization technique has been used. As a consequence, the objectivity of the computation with respect to mesh dependency is restored.

Rb-Sr dating of strain-induced mineral growth in two ductile shear zones in the western gneiss region of Nord-Troendelag, Central Norway

International Nuclear Information System (INIS)

Piasecki, M.A.; Cliff, R.A.

1988-01-01

In the Bjugn district of the northern part of the Western Gneiss Region, Nord-Troendelag, a basement gneiss-cover nappe boundary is marked by a thick zone of ductile shearing. In this zone a layer-parallel mylonitic fabric with related new mineral growth overprints and retrogresses a previous fabric associated with a granulite facies mineral assemblage. Related minor shear belts contain abundant new minerals and vein systems, including pegmatites, believed to represent strain-induced products formed at the time of the shearing movements. Central parts of two large muscovite books from such a pegmatite yielded Rb-Sr, Early to Middle Devonian ages of 389±6 Ma and 386±6 Ma, interpreted as indicating the approximate time of pegmatite formation and of the shearing. Small, matrix-size muscovite and biotite grains from the host mylonite gave ages of 378±6 Ma and 365±5 Ma, respectively, supposed to relate to post-shearing uplift and cooling

Interpretation of large-strain geophysical crosshole tests

International Nuclear Information System (INIS)

Drnevich, V.P.; Salgado, R.; Ashmawy, A.; Grant, W.P.; Vallenas, P.

1995-10-01

At sites in earthquake-prone areas, the nonlinear dynamic stress-strain behavior of soil with depth is essential for earthquake response analyses. A seismic crosshole test has been developed where large dynamic forces are applied in a borehole. These forces generate shear strains in the surrounding soil that are well into the nonlinear range. The shear strain amplitudes decrease with distance from the source. Velocity sensors located in three additional holes at various distances from the source hole measure the particle velocity and the travel time of the shear wave from the source. This paper provides an improved, systematic interpretation scheme for the data from these large-strain geophysical crosshole tests. Use is made of both the measured velocities at each sensor and the travel times. The measured velocity at each sensor location is shown to be a good measure of the soil particle velocity at that location. Travel times to specific features on the velocity time history, such as first crossover, are used to generate travel time curves for the waves which are nonlinear. At some distance the amplitudes reduce to where the stress-strain behavior is essentially linear and independent of strain amplitude. This fact is used together with the measurements at the three sensor locations in a rational approach for fitting curves of shear wave velocity versus distance from the source hole that allow the determination of the shear wave velocity and the shear strain amplitude at each of the sensor locations as well as the shear wave velocity associated with small-strain (linear) behavior. The method is automated using off-the-shelf PC-based software. The method is applied to large-strain crosshole tests performed as part of the studies for the design and construction of the proposed Multi-Function Waste Tank Facility planned for Hanford Site

Material model for shear of the buffer - evaluation of laboratory test results

International Nuclear Information System (INIS)

Boergesson, Lennart; Dueck, Ann; Johannesson, Lars-Erik

2010-12-01

The report describes the material model of bentonite used for analysing a rock shear through a deposition hole. The old model used in SR-Can has been considerably changed. The new reference model that has been developed for SR-Site is described and motivated. The relevant properties of the buffer that affect the response to a rock shear are (in addition to the bentonite type) the density (which yields a swelling pressure), the shear strength, the stiffness before the maximum shear stress is reached and the shear rate, which also affects the shear strength. Since the shear caused by an earthquake is very fast and the hydraulic conductivity of the bentonite is very low there is no possibility for the pore water in the water saturated bentonite to be redistributed. Since the compressibility of water and particles are negligible, the bentonite can be modelled as a solid material that cannot change volume but only exhibit shear deformations. A proper and simple model that behaves accordingly is a model with von Mises' stress modelled as a function of the strain (stress-strain model). The model is elastic-plastic with an E-modulus that determines the behaviour until the material starts yielding whereupon the plastic strain is modelled as a function of von Mises' stress and added to the elastic strain. Included in the model is also a strain rate dependency of the stress-strain relation, which ranges between the strain rates 10 -6 1/s 3 1/s. The reference material model is derived from a large number of laboratory tests made on different bentonites at different strain rates, densities and with different techniques. Since it cannot be excluded that the exchangeable cat-ions in the Na-bentonite MX-80 is exchanged to calcium-ions the Ca-bentonite Deponit CaN is proposed to be used as reference material. The overall conclusion is that a relevant and probably also slightly conservative material model of Ca-converted MX-80 is derived, presented and well motivated

Magnetization measurements reveal the local shear stiffness of hydrogels probed by ferromagnetic nanorods

Energy Technology Data Exchange (ETDEWEB)

Bender, P., E-mail: nano@p-bender.de; Tschöpe, A., E-mail: antsch@mx.uni-saarland.de; Birringer, R., E-mail: r.birringer@nano.uni-saarland.de

2014-12-15

The local mechanical coupling of ferromagnetic nanorods in hydrogels was characterized by magnetization measurements. Nickel nanorods were synthesized by the AAO-template method and embedded in gelatine hydrogels with mechanically soft or hard matrix properties determined by the gelatine weight fraction. By applying a homogeneous magnetic field during gelation the nanorods were aligned along the field resulting in uniaxially textured ferrogels. The magnetization curves of the soft ferrogel exhibited not only important similarities but also characteristic differences as compared to the hard ferrogel. The hystereses measured in a field parallel to the texture axis were almost identical for both samples indicating effective coupling of the nanorods with the polymer network. By contrast, measurements in a magnetic field perpendicular to the texture axis revealed a much higher initial susceptibility of the soft as compared to the hard ferrogel. This difference was attributed to the additional rotation of the nanorods allowed by the reduced shear modulus in the soft ferrogel matrix. Two methods for data analysis were presented which enabled us to determine the shear modulus of the gelatine matrix which was interpreted as a local rather than macroscopic quantity in consideration of the nanoscale of the probe particles. - Highlights: • Nanorods are embedded as magnetic probes in gelatine gels. • Elastic rotation of the rods can be induced by applying a homogeneous magnetic field. • Rod rotation has significant influence on the magnetization curves. • Two methods are presented to estimate the shear modulus of the matrix from the magnetization curves.

Enhancing tube hydroformability by reducing the local strain gradient at potential necking sites

International Nuclear Information System (INIS)

Shin, S. G. R.; Joo, B. D.; Moon, Y. H.; Tyne, C. J. Van

2014-01-01

Bursting in tube hydroforming is preceded by localized deformation, which is often called necking. The retardation of the initiation of necking is a means to enhance hydroformability. Since high strain gradients occur at necking sites, a decrease in local strain gradients is an effective way to retard the initiation of necking. In the current study, the expansion at potential necking sites was intentionally restricted in order to reduce the strain gradient at potential necking sites. From the strain distribution obtained from FEM, it is possible to determine strain concentrated zones, which are the potential necking sites. Prior to the hydroforming of a trailing arm, lead patch is attached to the tube where the strain concentration would occur. Due to the incompressibility of lead, the tube expansion is locally restricted, and the resultant strain extends to adjacent regions of the tube during hydroforming. After the first stage of hydroforming, the lead is removed from the tube, and the hydroforming continues to obtain the targeted shape without the local restriction. This method was successfully used to fabricate a complex shaped automotive trailing arm that had previously failed during traditional hydroforming processing.

Present-day crustal deformation and strain transfer in northeastern Tibetan Plateau

Science.gov (United States)

Li, Yuhang; Liu, Mian; Wang, Qingliang; Cui, Duxin

2018-04-01

The three-dimensional present-day crustal deformation and strain partitioning in northeastern Tibetan Plateau are analyzed using available GPS and precise leveling data. We used the multi-scale wavelet method to analyze strain rates, and the elastic block model to estimate slip rates on the major faults and internal strain within each block. Our results show that shear strain is strongly localized along major strike-slip faults, as expected in the tectonic extrusion model. However, extrusion ends and transfers to crustal contraction near the eastern margin of the Tibetan Plateau. The strain transfer is abrupt along the Haiyuan Fault and diffusive along the East Kunlun Fault. Crustal contraction is spatially correlated with active uplifting. The present-day strain is concentrated along major fault zones; however, within many terranes bounded by these faults, intra-block strain is detectable. Terranes having high intra-block strain rates also show strong seismicity. On average the Ordos and Sichuan blocks show no intra-block strain, but localized strain on the southwestern corner of the Ordos block indicates tectonic encroachment.

Numerical study on shear resisting mechanism for corroded RC box culverts

International Nuclear Information System (INIS)

Matsuo, Toyofumi; Matsumura, Takuro; Iwamori, Akiyuki

2013-01-01

This paper discusses the effects of reinforcing steel corrosion on the shear resisting mechanism of RC box culverts and the applicability of the material degradation model in a finite element method. First, in FEM analyses, loss of reinforcement section area and initial tension strain due to reinforcement corrosion, and deteriorated bond characteristics between reinforcement and concrete, were considered. Second, cyclic loading tests using full-scale corroded specimens were numerically analyzed. The analyzed crack patterns and load-displacement relationships up to the maximum load were observed to be in close agreement with the experiment results within the average corrosion ratio of 10% of primary reinforcement. The fact that corrosion cracks can importantly affect the progression of shear cracks and shear strength of RC beams was also found. On the other hand, we established that RC box culverts being statically indeterminate structures, sectional forces are redistributed after cracking damage, and local material deterioration has a minor effect on shear capacity. Furthermore, a parametric study was carried out for corroded RC box culverts using parameters such as size, steel corrosion location, and corrosion level. (author)

Relations Between Shear and Normal Stresses in a Step-Shear Experiment

DEFF Research Database (Denmark)

Hassager, Ole; Pedersen, Sven

1978-01-01

The Lodge-Meissner step-shear relation for simple fluids is examined. It is demonstrated that the relation depends critically on two assumptions for the integral expansion of the simple fluid: First, the use of the Cauchy strain tensor as strain measure, and second, that the memory functions...... are bounded. It is pointed out that many simple differential and integral models do not satisfy these criteria and hence predict deviations from the Lodge-Meissner relation....

Electronic properties of polycrystalline graphene under large local strain

International Nuclear Information System (INIS)

He, Xin; Tang, Ning; Duan, Junxi; Mei, Fuhong; Meng, Hu; Lu, Fangchao; Xu, Fujun; Yang, Xuelin; Gao, Li; Wang, Xinqiang; Shen, Bo; Ge, Weikun

2014-01-01

To explore the transport properties of polycrystalline graphene under large tensile strain, a strain device has been fabricated using piezocrystal to load local strain onto graphene, up to 22.5%. Ionic liquid gate whose capability of tuning carrier density being much higher than that of a solid gate is used to survey the transfer characteristics of the deformed graphene. The conductance of the Dirac point and field effect mobility of electrons and holes is found to decrease with increasing strain, which is attributed to the scattering of the graphene grain boundaries, the strain induced change of band structure, and defects. However, the transport gap is still not opened. Our study is helpful to evaluate the application of graphene in stretchable electronics.

Localization in Naturally Deformed Systems - the Default State?

Science.gov (United States)

Clancy White, Joseph

2017-04-01

Based on the extensive literature on localized rock deformation, conventional wisdom would interpret it to be a special behaviour within an anticipated background of otherwise uniform deformation. The latter notwithstanding, the rock record is so rife with transient (cyclic), heterogeneous deformation, notably shear localization, as to characterize localization as the anticipated 'normal' behaviour. The corollary is that steady, homogeneous deformation is significantly less common, and if achieved must reflect some special set of conditions that are not representative of the general case. An issue central to natural deformation is then not the existance of localized strain, but rather how the extant deformation processes scale across tectonic phenomena and in turn organize to enable a coherent(?) descripion of Earth deformation. Deformation is fundamentally quantized, discrete (diffusion, glide, crack propagation) and reliant on the defect state of rock-forming minerals. The strain energy distribution that drives thermo-mechanical responses is in the first instance established at the grain-scale where the non-linear interaction of defect-mediated micromechanical processes introduces heterogeneous behaviour described by various gradient theories, and evidenced by the defect microstructures of deformed rocks. Hence, the potential for non-uniform response is embedded within even quasi-uniform, monomineralic materials, seen, for example, in the spatially discrete evolution of dynamic recrystallization. What passes as homogeneous or uniform deformation at various scales is the aggregation of responses at some characteristic dimension at which heterogeneity is not registered or measured. Nevertheless, the aggregate response and associated normalized parameters (strain, strain rate) do not correspond to any condition actually experienced by the deforming material. The more common types of macroscopic heterogeneity promoting localization comprise mechanically contrasting

Dynamic Response and Failure Mechanism of Brittle Rocks Under Combined Compression-Shear Loading Experiments

Science.gov (United States)

Xu, Yuan; Dai, Feng

2018-03-01

A novel method is developed for characterizing the mechanical response and failure mechanism of brittle rocks under dynamic compression-shear loading: an inclined cylinder specimen using a modified split Hopkinson pressure bar (SHPB) system. With the specimen axis inclining to the loading direction of SHPB, a shear component can be introduced into the specimen. Both static and dynamic experiments are conducted on sandstone specimens. Given carefully pulse shaping, the dynamic equilibrium of the inclined specimens can be satisfied, and thus the quasi-static data reduction is employed. The normal and shear stress-strain relationships of specimens are subsequently established. The progressive failure process of the specimen illustrated via high-speed photographs manifests a mixed failure mode accommodating both the shear-dominated failure and the localized tensile damage. The elastic and shear moduli exhibit certain loading-path dependence under quasi-static loading but loading-path insensitivity under high loading rates. Loading rate dependence is evidently demonstrated through the failure characteristics involving fragmentation, compression and shear strength and failure surfaces based on Drucker-Prager criterion. Our proposed method is convenient and reliable to study the dynamic response and failure mechanism of rocks under combined compression-shear loading.

Normalized Rotational Multiple Yield Surface Framework (NRMYSF) stress-strain curve prediction method based on small strain triaxial test data on undisturbed Auckland residual clay soils

Science.gov (United States)

Noor, M. J. Md; Ibrahim, A.; Rahman, A. S. A.

2018-04-01

Small strain triaxial test measurement is considered to be significantly accurate compared to the external strain measurement using conventional method due to systematic errors normally associated with the test. Three submersible miniature linear variable differential transducer (LVDT) mounted on yokes which clamped directly onto the soil sample at equally 120° from the others. The device setup using 0.4 N resolution load cell and 16 bit AD converter was capable of consistently resolving displacement of less than 1µm and measuring axial strains ranging from less than 0.001% to 2.5%. Further analysis of small strain local measurement data was performed using new Normalized Multiple Yield Surface Framework (NRMYSF) method and compared with existing Rotational Multiple Yield Surface Framework (RMYSF) prediction method. The prediction of shear strength based on combined intrinsic curvilinear shear strength envelope using small strain triaxial test data confirmed the significant improvement and reliability of the measurement and analysis methods. Moreover, the NRMYSF method shows an excellent data prediction and significant improvement toward more reliable prediction of soil strength that can reduce the cost and time of experimental laboratory test.

Effects of Wheat Flour Dough’s Viscoelastic Level by Adding Glucose Oxidase on its Dynamic Shear Properties whatever the Strain Modes

Directory of Open Access Journals (Sweden)

Jean Didier Koffi Kouassi

2014-05-01

Full Text Available The objective of this work was to study the effects of wheat flour dough’s viscoelastic level by adding glucose oxidase (Gox on its rheological properties at dynamic shear strain mode to predict the final product quality. Dough does display a linear viscoelastic domain. Glucose oxidase (Gox was added to dough in order to enhance its viscoelasticity and to take into account the possible effects of this viscoelasticity on the results. Whatever the types of dough strain used G’ increased, tan δ decreased and led to less sticky dough. Wheat flour dough, an increase in G’ with extension may be associated to a strain-hardening phenomenon but the role of dough viscoelasticity is discussed.

Nucleation and evolution of strain-induced martensitic (b.c.c.) embryos and substructure in stainless steel: a transmission electron microscope study

International Nuclear Information System (INIS)

Staudhammer, K.P.; Hecker, S.S.; Murr, L.E.

1983-01-01

The deformation of type 304 stainless steel produces a preponderance of strain-induced /chi/ (b.c.c.) martensite, which nucleates as stable embryos at micro-shear band or twin-fault intersections as proposed by Olson and Cohen. The two intersecting micro-shear bands must have a specific defect (fault-displacement) structure, and for stable martensite embryos to form requires a minimal micro-shear band thickness ranging from 50-70 A. The critical nature of nucleation is influenced by the local temperature and strain. The structure, geometry, and morphology of strain-induced martensite embryos is essentially invariant regardless of the strain rate, strain state or temperature. Larger volume fractions of martensite evolve at large strains (greater than or equal to 20%) as a result of embryo coalescence to produce a blocky-type morphology. Martensite embryos and coalesced volume elements of /chi/ are frequently characterized by an irregular non-homogeneous distribution of smaller b.c.c. regimes which result from the irregular satisfaction of the necessary and specific fault-displacement requirements within a larger intersection volume

Multiscale mechanical integrity of human supraspinatus tendon in shear after elastin depletion.

Science.gov (United States)

Fang, Fei; Lake, Spencer P

2016-10-01

Human supraspinatus tendon (SST) exhibits region-specific nonlinear mechanical properties under tension, which have been attributed to its complex multiaxial physiological loading environment. However, the mechanical response and underlying multiscale mechanism regulating SST behavior under other loading scenarios are poorly understood. Furthermore, little is known about the contribution of elastin to tendon mechanics. We hypothesized that (1) SST exhibits region-specific shear mechanical properties, (2) fiber sliding is the predominant mode of local matrix deformation in SST in shear, and (3) elastin helps maintain SST mechanical integrity by facilitating force transfer among collagen fibers. Through the use of biomechanical testing and multiphoton microscopy, we measured the multiscale mechanical behavior of human SST in shear before and after elastase treatment. Three distinct SST regions showed similar stresses and microscale deformation. Collagen fiber reorganization and sliding were physical mechanisms observed as the SST response to shear loading. Measures of microscale deformation were highly variable, likely due to a high degree of extracellular matrix heterogeneity. After elastase treatment, tendon exhibited significantly decreased stresses under shear loading, particularly at low strains. These results show that elastin contributes to tendon mechanics in shear, further complementing our understanding of multiscale tendon structure-function relationships. Copyright © 2016 Elsevier Ltd. All rights reserved.

Lattice shear distortions in fluorite structure oxides

International Nuclear Information System (INIS)

Faber, J. Jr.; Mueller, M.H.; Hitterman, R.L.

1979-01-01

Crystallographic shear distortions have been observed in fluorite structure, single crystals of UO 2 and Zr(Ca)O 2 /sub-x/ by neutron-diffraction techniques. These distortions localize on the oxygen sublattice and do not require the presence of an external strain. The internal rearrangement mode in UO 2 is a transverse, zone boundary q vector = 2π/a (0.5, 0.0) deformation with amplitude 0.014 A. In Zr(Ca)O/sub 2-x/, the mode is a longitudinal, q vector = 2-/a (0,0,0.5) deformation with amplitude 0.23 A. Cation-anion elastic interactions dominate in selecting the nature of the internal distortion

Local parametric instability near elliptic points in vortex flows under shear deformation

Energy Technology Data Exchange (ETDEWEB)

Koshel, Konstantin V., E-mail: kvkoshel@poi.dvo.ru [Pacific Oceanological Institute, FEB RAS, 43, Baltiyskaya Street, Vladivostok 690041 (Russian Federation); Institute of Applied Mathematics, FEB RAS, 7, Radio Street, Vladivostok 690022 (Russian Federation); Far Eastern Federal University, 8, Sukhanova Street, Vladivostok 690950 (Russian Federation); Ryzhov, Eugene A., E-mail: ryzhovea@gmail.com [Pacific Oceanological Institute, FEB RAS, 43, Baltiyskaya Street, Vladivostok 690041 (Russian Federation)

2016-08-15

The dynamics of two point vortices embedded in an oscillatory external flow consisted of shear and rotational components is addressed. The region associated with steady-state elliptic points of the vortex motion is established to experience local parametric instability. The instability forces the point vortices with initial positions corresponding to the steady-state elliptic points to move in spiral-like divergent trajectories. This divergent motion continues until the nonlinear effects suppress their motion near the region associated with the steady-state separatrices. The local parametric instability is then demonstrated not to contribute considerably to enhancing the size of the chaotic motion regions. Instead, the size of the chaotic motion region mostly depends on overlaps of the nonlinear resonances emerging in the perturbed system.

Friction of Shear-Fracture Zones

Science.gov (United States)

Riikilä, T. I.; Pylväinen, J. I.; Åström, J.

2017-12-01

A shear fracture of brittle solids under compression undergoes a substantial evolution from the initial microcracking to a fully formed powder-filled shear zone. Experiments covering the entire process are relatively easy to conduct, but they are very difficult to investigate in detail. Numerically, the large strain limit has remained a challenge. An efficient simulation model and a custom-made experimental device are employed to test to what extent a shear fracture alone is sufficient to drive material to spontaneous self-lubrication. A "weak shear zone" is an important concept in geology, and a large number of explanations, specific for tectonic conditions, have been proposed. We demonstrate here that weak shear zones are far more general, and that their emergence only demands that a microscopic, i.e., fragment-scale, stress relaxation mechanism develops during the fracture process.

Improved failure prediction in forming simulations through pre-strain mapping

Science.gov (United States)

Upadhya, Siddharth; Staupendahl, Daniel; Heuse, Martin; Tekkaya, A. Erman

2018-05-01

The sensitivity of sheared edges of advanced high strength steel (AHSS) sheets to cracking during subsequent forming operations and the difficulty to predict this failure with any degree of accuracy using conventionally used FLC based failure criteria is a major problem plaguing the manufacturing industry. A possible method that allows for an accurate prediction of edge cracks is the simulation of the shearing operation and carryover of this model into a subsequent forming simulation. But even with an efficient combination of a solid element shearing operation and a shell element forming simulation, the need for a fine mesh, and the resulting high computation time makes this approach not viable from an industry point of view. The crack sensitivity of sheared edges is due to work hardening in the shear-affected zone (SAZ). A method to predict plastic strains induced by the shearing process is to measure the hardness after shearing and calculate the ultimate tensile strength as well as the flow stress. In combination with the flow curve, the relevant strain data can be obtained. To eliminate the time-intensive shearing simulation necessary to obtain the strain data in the SAZ, a new pre-strain mapping approach is proposed. The pre-strains to be mapped are, hereby, determined from hardness values obtained in the proximity of the sheared edge. To investigate the performance of this approach the ISO/TS 16630 hole expansion test was simulated with shell elements for different materials, whereby the pre-strains were mapped onto the edge of the hole. The hole expansion ratios obtained from such pre-strain mapped simulations are in close agreement with the experimental results. Furthermore, the simulations can be carried out with no increase in computation time, making this an interesting and viable solution for predicting edge failure due to shearing.

Shear Piezoelectricity in Poly(vinylidenefluoride-co-trifluoroethylene): Full Piezotensor Coefficients by Molecular Modeling, Biaxial Transverse Response, and Use in Suspended Energy-Harvesting Nanostructures.

Science.gov (United States)

Persano, Luana; Catellani, Alessandra; Dagdeviren, Canan; Ma, Yinji; Guo, Xiaogang; Huang, Yonggang; Calzolari, Arrigo; Pisignano, Dario

2016-09-01

The intrinsic flexible character of polymeric materials causes remarkable strain deformations along directions perpendicular to the applied stress. The biaxial response in the shear piezoelectricity of polyvinylidenefluoride copolymers is analyzed and their full piezoelectric tensors are provided. The microscopic shear is exploited in single suspended nanowires bent by localized loading to couple flexural deformation and transverse piezoelectric response. © 2016 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Strain localisation in mechanically layered rocks beneath detachment zones: insights from numerical modelling

Directory of Open Access Journals (Sweden)

L. Le Pourhiet

2013-04-01

Full Text Available We have designed a series of fully dynamic numerical simulations aimed at assessing how the orientation of mechanical layering in rocks controls the orientation of shear bands and the depth of penetration of strain in the footwall of detachment zones. Two parametric studies are presented. In the first one, the influence of stratification orientation on the occurrence and mode of strain localisation is tested by varying initial dip of inherited layering in the footwall with regard to the orientation of simple shear applied at the rigid boundary simulating a rigid hanging wall, all scaling and rheological parameter kept constant. It appears that when Mohr–Coulomb plasticity is being used, shear bands are found to localise only when the layering is being stretched. This corresponds to early deformational stages for inital layering dipping in the same direction as the shear is applied, and to later stages for intial layering dipping towards the opposite direction of shear. In all the cases, localisation of the strain after only γ=1 requires plastic yielding to be activated in the strong layer. The second parametric study shows that results are length-scale independent and that orientation of shear bands is not sensitive to the viscosity contrast or the strain rate. However, decreasing or increasing strain rate is shown to reduce the capacity of the shear zone to localise strain. In the later case, the strain pattern resembles a mylonitic band but the rheology is shown to be effectively linear. Based on the results, a conceptual model for strain localisation under detachment faults is presented. In the early stages, strain localisation occurs at slow rates by viscous shear instabilities but as the layered media is exhumed, the temperature drops and the strong layers start yielding plastically, forming shear bands and localising strain at the top of the shear zone. Once strain localisation has occured, the deformation in the shear band becomes

Strain Pattern in Supercooled Liquids

Science.gov (United States)

Illing, Bernd; Fritschi, Sebastian; Hajnal, David; Klix, Christian; Keim, Peter; Fuchs, Matthias

2016-11-01

Investigations of strain correlations at the glass transition reveal unexpected phenomena. The shear strain fluctuations show an Eshelby-strain pattern [˜cos (4 θ ) /r2 ], characteristic of elastic response, even in liquids, at long times. We address this using a mode-coupling theory for the strain fluctuations in supercooled liquids and data from both video microscopy of a two-dimensional colloidal glass former and simulations of Brownian hard disks. We show that the long-ranged and long-lived strain signatures follow a scaling law valid close to the glass transition. For large enough viscosities, the Eshelby-strain pattern is visible even on time scales longer than the structural relaxation time τ and after the shear modulus has relaxed to zero.

The ultimate fate of a synmagmatic shear zone. Interplay between rupturing and ductile flow in a cooling granite pluton

Science.gov (United States)

Zibra, I.; White, J. C.; Menegon, L.; Dering, G.; Gessner, K.

2018-05-01

The Neoarchean Cundimurra Pluton (Yilgarn Craton, Western Australia) was emplaced incrementally along the transpressional Cundimurra Shear Zone. During syndeformational cooling, discrete networks of cataclasites and ultramylonites developed in the narrowest segment of the shear zone, showing the same kinematics as the earlier synmagmatic structures. Lithological boundaries between aplite/pegmatite veins and host granitic gneiss show more intense pre-cataclasite fabrics than homogeneous material, and these boundaries later became the preferred sites of shear rupture and cataclasite nucleation. Transient ductile instabilities established along lithological boundaries culminated in shear rupture at relatively high temperature (∼500-600 °C). Here, tensile fractures at high angles from the fault plane formed asymmetrically on one side of the fault, indicating development during seismic rupture, establishing the oldest documented earthquake on Earth. Tourmaline veins were emplaced during brittle shearing, but fluid pressure probably played a minor role in brittle failure, as cataclasites are in places tourmaline-free. Subsequent ductile deformation localized in the rheologically weak tourmaline-rich aggregates, forming ultramylonites that deformed by grain-size sensitive creep. The shape and width of the pluton/shear zone and the regime of strain partitioning, induced by melt-present deformation and established during pluton emplacement, played a key role in controlling the local distribution of brittle and then ductile subsolidus structures.

Localized modelling and feedback control of linear instabilities in 2-D wall bounded shear flows

Science.gov (United States)

Tol, Henry; Kotsonis, Marios; de Visser, Coen

2016-11-01

A new approach is presented for control of instabilities in 2-D wall bounded shear flows described by the linearized Navier-Stokes equations (LNSE). The control design accounts both for spatially localized actuators/sensors and the dominant perturbation dynamics in an optimal control framework. An inflow disturbance model is proposed for streamwise instabilities that drive laminar-turbulent transition. The perturbation modes that contribute to the transition process can be selected and are included in the control design. A reduced order model is derived from the LNSE that captures the input-output behavior and the dominant perturbation dynamics. This model is used to design an optimal controller for suppressing the instability growth. A 2-D channel flow and a 2-D boundary layer flow over a flat plate are considered as application cases. Disturbances are generated upstream of the control domain and the resulting flow perturbations are estimated/controlled using wall shear measurements and localized unsteady blowing and suction at the wall. It will be shown that the controller is able to cancel the perturbations and is robust to unmodelled disturbances.

Size effects and strain localization in atomic-scale cleavage modeling

International Nuclear Information System (INIS)

Elsner, B A M; Müller, S

2015-01-01

In this work, we study the adhesion and decohesion of Cu(1 0 0) surfaces using density functional theory (DFT) calculations. An upper stress to surface decohesion is obtained via the universal binding energy relation (UBER), but the model is limited to rigid separation of bulk-terminated surfaces. When structural relaxations are included, an unphysical size effect arises if decohesion is considered to occur as soon as the strain energy equals the energy of the newly formed surfaces. We employ the nudged elastic band (NEB) method to show that this size effect is opposed by a size-dependency of the energy barriers involved in the transition. Further, we find that the transition occurs via a localization of bond strain in the vicinity of the cleavage plane, which resembles the strain localization at the tip of a sharp crack that is predicted by linear elastic fracture mechanics. (paper)

Numerical Simulations of the Effects of a Tidal Turbine Array on Near-Bed Velocity and Local Bed Shear Stress

Directory of Open Access Journals (Sweden)

Philip A. Gillibrand

2016-10-01

Full Text Available We apply a three-dimensional hydrodynamic model to consider the potential effects of energy extraction by an array of tidal turbines on the ambient near-bed velocity field and local bed shear stress in a coastal channel with strong tidal currents. Local bed shear stress plays a key role in local sediment dynamics. The model solves the Reynold-averaged Navier-Stokes (RANS equations on an unstructured mesh using mixed finite element and finite volume techniques. Tidal turbines are represented through an additional form drag in the momentum balance equation, with the thrust imparted and power generated by the turbines being velocity dependent with appropriate cut-in and cut-out velocities. Arrays of 1, 4 and 57 tidal turbines, each of 1.5 MW capacity, were simulated. Effects due to a single turbine and an array of four turbines were negligible. The main effect of the array of 57 turbines was to cause a shift in position of the jet through the tidal channel, as the flow was diverted around the tidal array. The net effect of this shift was to increase near-bed velocities and bed shear stress along the northern perimeter of the array by up to 0.8 m·s−1 and 5 Pa respectively. Within the array and directly downstream, near-bed velocities and bed shear stress were reduced by similar amounts. Changes of this magnitude have the potential to modify the known sand and shell banks in the region. Continued monitoring of the sediment distributions in the region will provide a valuable dataset on the impacts of tidal energy extraction on local sediment dynamics. Finally, the mean power generated per turbine is shown to decrease as the turbine array increased in size.

Numerical analysis of strain localization for transversely isotropic model with non-coaxial flow rule

Science.gov (United States)

Wei, Ding; Cong-cong, Yu; Chen-hui, Wu; Zheng-yi, Shu

2018-03-01

To analyse the strain localization behavior of geomaterials, the forward Euler schemes and the tangent modulus matrix are formulated based on the transversely isotropic yield criterion with non-coaxial flow rule developed by Lade, the program code is implemented based on the user subroutine (UMAT) of ABAQUS. The influence of the material principal direction on the strain localization and the bearing capacity of the structure are investigated and analyzed. Numerical results show the validity and performance of the proposed model in simulating the strain localization behavior of geostructures.

An evaluation of the lap-shear test for Sn-rich solder/Cu couples: Experiments and simulation

Science.gov (United States)

Chawla, N.; Shen, Y.-L.; Deng, X.; Ege, E. S.

2004-12-01

The lap-shear technique is commonly used to evaluate the shear, creep, and thermal fatigue behavior of solder joints. We have conducted a parametric experimental and modeling study, on the effect of testing and geometrical parameters on solder/copper joint response in lap-shear. It was shown that the farfield applied strain is quite different from the actual solder strain (measured optically). Subtraction of the deformation of the Cu substrate provides a reasonable approximation of the solder strain in the elastic regime, but not in the plastic regime. Solder joint thickness has a profound effect on joint response. The solder response moves progressively closer to “true” shear response with increasing joint thickness. Numerical modeling using finite-element analyses were performed to rationalize the experimental findings. The same lap-shear configuration was used in the simulation. The input response for solder was based on the experimental tensile test result on bulk specimens. The calculated shear response, using both the commonly adopted far-field measure and the actual shear strain in solder, was found to be consistent with the trends observed in the lap-shear experiments. The geometric features were further explored to provide physical insight into the problem. Deformation of the substrate was found to greatly influence the shear behavior of the solder.

Rupture prediction for induction bends under opening mode bending with emphasis on strain localization

International Nuclear Information System (INIS)

Mitsuya, Masaki; Sakanoue, Takashi

2015-01-01

This study focuses on the opening mode of induction bends; this mode represents the deformation outside a bend. Bending experiments on induction bends are shown and the manner of failure of these bends was investigated. Ruptures occur at the intrados of the bends, which undergo tensile stress, and accompany the local reduction of wall thickness, i.e., necking that indicates strain localization. By implementing finite element analysis (FEA), it was shown that the rupture is dominated not by the fracture criterion of material but by the initiation of strain localization that is a deformation characteristic of the material. These ruptures are due to the rapid increase of local strain after the initiation of strain localization and suddenly reach the fracture criterion. For the evaluation of the deformability of the bends, a method based on FEA that can predict the displacement at the rupture is proposed. We show that the yield surface shape and the true stress–strain relationship after uniform elongation have to be defined on the basis of the actual properties of the bend material. The von Mises yield criterion, which is commonly used in cases of elastic–plastic FEA, could not predict the rupture and overestimated the deformability. In contrast, a yield surface obtained by performing tensile tests on a biaxial specimen could predict the rupture. The prediction of the rupture was accomplished by an inverse calibration method that determined the true stress-strain relationship after uniform elongation. As an alternative to the inverse calibration, a simple extrapolation method of the true stress-strain relationship after uniform elongation which can predict the rupture is proposed. - Highlights: • A method based on FEA that can predict the displacement at the rupture is proposed. • The yield surface shape and the true stress–strain have to be defined precisely. • The von Mises yield criterion overestimated the deformability. • The ruptures are due to the

Thermomechanical Studies of Yielding and Strain Localization Phenomena of Gum Metal under Tension

Directory of Open Access Journals (Sweden)

Elżbieta A. Pieczyska

2018-04-01

Full Text Available This paper presents results of investigation of multifunctional β-Ti alloy Gum Metal subjected to tension at various strain rates. Digital image correlation was used to determine strain distributions and stress-strain curves, while infrared camera allowed for us to obtain the related temperature characteristics of the specimen during deformation. The mechanical curves completed by the temperature changes were applied to analyze the subsequent stages of the alloy loading. Elastic limit, recoverable strain, and development of the strain localization were studied. It was found that the maximal drop in temperature, which corresponds to the yield limit of solid materials, was referred to a significantly lower strain value in the case of Gum Metal in contrast to its large recoverable strain. The temperature increase proves a dissipative character of the process and is related to presence of ω and α″ phases induced during the alloy fabrication and their exothermic phase transformations activated under loading. During plastic deformation, both the strain and temperature distributions demonstrate that strain localization for higher strain rates starts nucleating just after the yield limit leading to specimen necking and rupture. Macroscopically, it is exhibited as softening of the stress-strain curve in contrast to the strain hardening observed at lower strain rates.

Sense of shear and displacement estimates in the Abeibara-Rarhous late Pan-African shear zone, Adrar des Iforas, Mali

Science.gov (United States)

Boullier, Anne-Marie

The late Pan-African Abeibara-Rarhous shear zone in the Adrar des Iforas (Mali) is described and studied with the aim of defining the direction, sense of movement and amount of displacement along the zone. It is a strike-slip shear zone, the dextral sense of which is demonstrated at the scale of the map by the rotation of the related mylonitic foliation and at the scale of the thin section with characteristic microstructures. Preferred orientation of quartz c-axes is tentatively used; three quartz-rich samples of 35% or more quartz indicate dextral strike-slip movement, but other samples do not show preferred orientation of quartz c-axes. Strain measurements have been performed on one half of the shear zone using established techniques and a new technique using the thickness of mylonitic layering. The results vary along the length of the shear zone when using the same method and for the same cross-section when using the three methods together. A mean value of 4 km is obtained for total displacement which is low when considering the apparent width of the shear zone. This result is discussed in view of the assumptions involved in the strain estimation. The tectonic history of the Abeibara-Rarhous shear zone and its significance in the Trans-Saharan Pan-African collisional belt are discussed.

Evaluation of local strain in Si using UV-Raman spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Ogura, Atsushi [School of Science and Technology, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki, Kanagawa 214-8571 (Japan)], E-mail: a_ogura@isc.meiji.ac.jp; Kosemura, Daisuke; Takei, Munehisa [School of Science and Technology, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki, Kanagawa 214-8571 (Japan); Uchida, Hidetsugu; Hattori, Nobuyoshi [Semiconductor Technology Academic Research Center, 3-17-2 Shinyokohama, Kouhoku-ku, Yokohama 220-0033 (Japan); Yoshimaru, Masaki [Semiconductor Business Group, Sony Corporation, Atsugi Tec., 4-14-1 Asahi-cho, Atsugi-shi, Kanagawa 243-0014 (Japan); Mayuzumi, Satoru [School of Science and Technology, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki, Kanagawa 214-8571 (Japan); Semiconductor Business Group, Sony Corporation, Atsugi Tec., 4-14-1 Asahi-cho, Atsugi-shi, Kanagawa 243-0014 (Japan); Wakabayashi, Hitoshi [Semiconductor Business Group, Sony Corporation, Atsugi Tec., 4-14-1 Asahi-cho, Atsugi-shi, Kanagawa 243-0014 (Japan)

2009-03-15

'Strained-Si', in which intentional strain is introduced in Si crystal to improve carrier mobility by using a modulated band structure, is recognized as one of the most important technologies in post-scaling-generation LSIs. Strain-evaluation technology to probe strain in shallow surfaces that correspond to the channels of MOSFETs is crucial to achieving strained-Si technology. In this paper, we introduce the results we obtained by evaluating strain with the new UV-Raman spectroscopy we developed. Quasi-line shape illumination enabled Raman measurements with 200-nm intervals on the sample. The local-strain mechanism caused by SiN stressors covering a MOSFET was clarified by measuring one-dimensional strain profiles induced by patterned SiN film on Si. We also demonstrated that the induced strain was proportional to the inner stresses of SiN film and that it is more effective to introduce strain in SOI substrates than in bulk substrates. In the evaluation of a actual device fabricated by using the gate-last process in which strain was significantly enhanced after the dummy gate was removed, the size effect, i.e., an increase in induced strain with a decrease in gate length, was confirmed through one-dimensional strain-profile measurements with various gate lengths.

Evaluation of local strain in Si using UV-Raman spectroscopy

International Nuclear Information System (INIS)

Ogura, Atsushi; Kosemura, Daisuke; Takei, Munehisa; Uchida, Hidetsugu; Hattori, Nobuyoshi; Yoshimaru, Masaki; Mayuzumi, Satoru; Wakabayashi, Hitoshi

2009-01-01

'Strained-Si', in which intentional strain is introduced in Si crystal to improve carrier mobility by using a modulated band structure, is recognized as one of the most important technologies in post-scaling-generation LSIs. Strain-evaluation technology to probe strain in shallow surfaces that correspond to the channels of MOSFETs is crucial to achieving strained-Si technology. In this paper, we introduce the results we obtained by evaluating strain with the new UV-Raman spectroscopy we developed. Quasi-line shape illumination enabled Raman measurements with 200-nm intervals on the sample. The local-strain mechanism caused by SiN stressors covering a MOSFET was clarified by measuring one-dimensional strain profiles induced by patterned SiN film on Si. We also demonstrated that the induced strain was proportional to the inner stresses of SiN film and that it is more effective to introduce strain in SOI substrates than in bulk substrates. In the evaluation of a actual device fabricated by using the gate-last process in which strain was significantly enhanced after the dummy gate was removed, the size effect, i.e., an increase in induced strain with a decrease in gate length, was confirmed through one-dimensional strain-profile measurements with various gate lengths.

Experimental determination of the stress/strain situation in a sheared tunnel model with canister

International Nuclear Information System (INIS)

Pusch, R.

1978-03-01

A previous report concerned a technical matter which could be of great importance as regards the mechanical strength of canisters embedded in a bentonite/quartz buffer mass, i.e. the effect of a differential movement triggered by a critical deviatoric stress condition. Even if this is extremely unlikeley to occur it was considered to be of importance to verify the theoretical expressions for the maximum bending moment and maximum shear force. A special reason was to test the hypothesis that the contact pressure would soon reach a high value and then stay fairly constant when the displacement increased. The theoretical approach requires that the stress/strain properties of the fill are thoroghly investigated and described in therms of a mathematical model. Experience shows that this may be a tedions and difficult task. (L.E.)

Experimental and numerical study of plastic shear instability under high-speed loading conditions

International Nuclear Information System (INIS)

Sokovikov, Mikhail; Chudinov, Vasiliy; Bilalov, Dmitry; Oborin, Vladimir; Uvarov, Sergey; Plekhov, Oleg; Terekhina, Alena; Naimark, Oleg

2014-01-01

The behavior of specimens dynamically loaded during the split Hopkinson (Kolsky) bar tests in a regime close to simple shear conditions was studied. The lateral surface of the specimens was investigated in a real-time mode with the aid of a high-speed infra-red camera CEDIP Silver 450M. The temperature field distribution obtained at different time made it possible to trace the evolution of plastic strain localization. The process of target perforation involving plug formation and ejection was examined using a high-speed infra-red camera and a VISAR velocity measurement system. The microstructure of tested specimens was analyzed using an optical interferometer-profilometer and a scanning electron microscope. The development of plastic shear instability regions has been simulated numerically

Shear banding, discontinuous shear thickening, and rheological phase transitions in athermally sheared frictionless disks

Science.gov (United States)

Vâgberg, Daniel; Olsson, Peter; Teitel, S.

2017-05-01

We report on numerical simulations of simple models of athermal, bidisperse, soft-core, massive disks in two dimensions, as a function of packing fraction ϕ , inelasticity of collisions as measured by a parameter Q , and applied uniform shear strain rate γ ˙. Our particles have contact interactions consisting of normally directed elastic repulsion and viscous dissipation, as well as tangentially directed viscous dissipation, but no interparticle Coulombic friction. Mapping the phase diagram in the (ϕ ,Q ) plane for small γ ˙, we find a sharp first-order rheological phase transition from a region with Bagnoldian rheology to a region with Newtonian rheology, and show that the system is always Newtonian at jamming. We consider the rotational motion of particles and demonstrate the crucial importance that the coupling between rotational and translational degrees of freedom has on the phase structure at small Q (strongly inelastic collisions). At small Q , we show that, upon increasing γ ˙, the sharp Bagnoldian-to-Newtonian transition becomes a coexistence region of finite width in the (ϕ ,γ ˙) plane, with coexisting Bagnoldian and Newtonian shear bands. Crossing this coexistence region by increasing γ ˙ at fixed ϕ , we find that discontinuous shear thickening can result if γ ˙ is varied too rapidly for the system to relax to the shear-banded steady state corresponding to the instantaneous value of γ ˙.

A microstructural study of SAFOD gouge from actively creeping San Andreas Fault zone; Implications for shear localization models

Science.gov (United States)

Blackburn, E. D.; Hadizadeh, J.; Babaie, H. A.

2009-12-01

The prevailing models of shear localization in fault gouges are mainly based on experimental aggregates that necessarily neglect the effects of chemical and mechanical maturation with time. The SAFOD cores have provided a chance to test whether cataclasis as a deformation mechanism and factors such as porosity and particle size, critical in some existing shear localization models continue to be critical in mature gouges. We studied a core sample from 3194m MD in the SAFOD phase 3, which consists of intensely foliated shale-siltstone cataclasites in contact with less deformed shale. Microstructures were studied in 3 perpendicular planes with reference to foliation using high resolution scanning electron microscopy, cathodoluminescence imaging, X-ray fluorescence mapping, and energy dispersive X-ray spectroscopy. The cataclastic foliation, recognizable at length scales >100 μm, is primarily defined by bands of clay gouge with distinct microstructure, clay content, and porosity. Variations in elemental composition and porosity of the clay gouge were measured continuously across the foliation. Prominent features within the foliation bands include lens-shaped clusters of highly brecciated and veined siltstone fragments, pyrite smears, and pyrite-cemented cataclasites. The microstructural relations and chemical data provide clear evidence of multiple episodes of veining and deformation with some possibility of relative age determination for the episodes. There is evidence of syn-deformation hydrothermal changes including growth and brittle shear of pyrite, alteration of host shale clays to illite-smectite clays and Fe-rich smectite. Evidence of grain-boundary corrosion of non-clay mineral fragments suggests pressure solution creep. The gouge porosity estimates varied from 0-18% (about 3% in less deformed shale) with the highest value in the bands with abundant siltstone fragments. The banding is mechanically significant since it pervasively segregates the gouge into

Fatigue Life Prediction of High Modulus Asphalt Concrete Based on the Local Stress-Strain Method

Directory of Open Access Journals (Sweden)

Mulian Zheng

2017-03-01

Full Text Available Previously published studies have proposed fatigue life prediction models for dense graded asphalt pavement based on flexural fatigue test. This study focused on the fatigue life prediction of High Modulus Asphalt Concrete (HMAC pavement using the local strain-stress method and direct tension fatigue test. First, the direct tension fatigue test at various strain levels was conducted on HMAC prism samples cut from plate specimens. Afterwards, their true stress-strain loop curves were obtained and modified to develop the strain-fatigue life equation. Then the nominal strain of HMAC course determined using finite element method was converted into local strain using the Neuber method. Finally, based on the established fatigue equation and converted local strain, a method to predict the pavement fatigue crack initiation life was proposed and the fatigue life of a typical HMAC overlay pavement which runs a risk of bottom-up cracking was predicted and validated. Results show that the proposed method was able to produce satisfactory crack initiation life.

Modeling Shock Induced Plasticity in Copper Single Crystal: Numerical and Strain Localization Issues

International Nuclear Information System (INIS)

Shehadeh, M

2011-01-01

Multiscale dislocation dynamics plasticity (MDDP) simulations are carried out to address the following issues in modeling shock-induced plasticity: 1- the effect of finite element (FE) boundary conditions on shock wave characteristics and wave-dislocation interaction, 2- the effect of the evolution of the dislocation microstructure on lattice rotation and strain localization. While uniaxial strain is achieved with high accuracy using confined boundary condition, periodic boundary condition yields a disturbed wave profile due the edge effect. Including lattice rotation in the analysis leads to higher dislocation density and more localized plastic strain. (author)

Nonlinear interaction of Rayleigh--Taylor and shear instabilities

International Nuclear Information System (INIS)

Finn, J.M.

1993-01-01

Results on the nonlinear behavior of the Rayleigh--Taylor instability and consequent development of shear flow by the shear instability [Phys. Fluids B 4, 488 (1992)] are presented. It is found that the shear flow is generated at sufficient amplitude to reduce greatly the convective transport. For high viscosity, the time-asymptotic state consists of an equilibrium with shear flow and vortex flow (with islands, or ''cat's eyes''), or a relaxation oscillation involving an interplay between the shear instability and the Rayleigh--Taylor instability in the presence of shear. For low viscosity, the dominant feature is a high-frequency nonlinear standing wave consisting of convective vortices localized near the top and bottom boundaries. The localization of these vortices is due to the smaller shear near the boundary regions. The convective transport is largest around these convective vortices near the boundary and there is a region of good confinement near the center. The possible relevance of this behavior to the H mode and edge-localized modes (ELM's) in the tokamak edge region is discussed

Growth of extrusions in localized cyclic plastic straining

Czech Academy of Sciences Publication Activity Database

Polák, Jaroslav; Sauzay, M.

2009-01-01

Roč. 500, č. 1-2 (2009), s. 122-129 ISSN 0921-5093 R&D Projects: GA ČR GA101/07/1500 Institutional research plan: CEZ:AV0Z20410507 Keywords : extrusion * strain localization * persistent slip band * vacancy Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 1.901, year: 2009

Shear-induced breaking of cages in colloidal glasses: Scattering experiments and mode coupling theory

Energy Technology Data Exchange (ETDEWEB)

Amann, Christian P., E-mail: Christian.2.Amann@uni-konstanz.de; Fuchs, Matthias, E-mail: Matthias.Fuchs@uni-konstanz.de [Fachbereich Physik, Universität Konstanz, 78457 Konstanz (Germany); Denisov, Dmitry; Dang, Minh Triet; Schall, Peter [Van der Waals-Zeeman Institute, University of Amsterdam, Amsterdam (Netherlands); Struth, Bernd [Deutsches Elektronen-Synchrotron, Hamburg (Germany)

2015-07-21

We employ x-ray scattering on sheared colloidal suspensions and mode coupling theory to study structure factor distortions of glass-forming systems under shear. We find a transition from quadrupolar elastic distortion at small strains to quadrupolar and hexadecupolar modes in the stationary state. The latter are interpreted as signatures of plastic rearrangements in homogeneous, thermalized systems. From their transient evolution with strain, we identify characteristic strain and length-scale values where these plastic rearrangements dominate. This characteristic strain coincides with the maximum of the shear stress versus strain curve, indicating the proliferation of plastic flow. The hexadecupolar modes dominate at the wavevector of the principal peak of the equilibrium structure factor that is related to the cage-effect in mode coupling theory. We hence identify the structural signature of plastic flow of glasses.

Shear-induced breaking of cages in colloidal glasses: Scattering experiments and mode coupling theory

International Nuclear Information System (INIS)

Amann, Christian P.; Fuchs, Matthias; Denisov, Dmitry; Dang, Minh Triet; Schall, Peter; Struth, Bernd

2015-01-01

We employ x-ray scattering on sheared colloidal suspensions and mode coupling theory to study structure factor distortions of glass-forming systems under shear. We find a transition from quadrupolar elastic distortion at small strains to quadrupolar and hexadecupolar modes in the stationary state. The latter are interpreted as signatures of plastic rearrangements in homogeneous, thermalized systems. From their transient evolution with strain, we identify characteristic strain and length-scale values where these plastic rearrangements dominate. This characteristic strain coincides with the maximum of the shear stress versus strain curve, indicating the proliferation of plastic flow. The hexadecupolar modes dominate at the wavevector of the principal peak of the equilibrium structure factor that is related to the cage-effect in mode coupling theory. We hence identify the structural signature of plastic flow of glasses

Shear-induced breaking of cages in colloidal glasses: Scattering experiments and mode coupling theory.

Science.gov (United States)

Amann, Christian P; Denisov, Dmitry; Dang, Minh Triet; Struth, Bernd; Schall, Peter; Fuchs, Matthias

2015-07-21

We employ x-ray scattering on sheared colloidal suspensions and mode coupling theory to study structure factor distortions of glass-forming systems under shear. We find a transition from quadrupolar elastic distortion at small strains to quadrupolar and hexadecupolar modes in the stationary state. The latter are interpreted as signatures of plastic rearrangements in homogeneous, thermalized systems. From their transient evolution with strain, we identify characteristic strain and length-scale values where these plastic rearrangements dominate. This characteristic strain coincides with the maximum of the shear stress versus strain curve, indicating the proliferation of plastic flow. The hexadecupolar modes dominate at the wavevector of the principal peak of the equilibrium structure factor that is related to the cage-effect in mode coupling theory. We hence identify the structural signature of plastic flow of glasses.

Transformation of localized necking of strain space into stress space for advanced high strength steel sheet

Science.gov (United States)

Nakwattanaset, Aeksuwat; Suranuntchai, Surasak

2018-03-01

Normally, Forming Limit Curves (FLCs) can’t explain for shear fracture better than Damage Curve, this article aims to show the experimental of Forming Limit Curve (FLC) for Advanced High Strength Steel (AHSS) sheets grade JAC780Y with the Nakazima forming test and tensile tests of different sample geometries. From these results, the Forming Limit Curve (strain space) was transformed to damage curve (stress space) between plastic strain and stress triaxiality. Therefore, Stress space transformed using by Hill-48 and von-Mises yield function. This article shows that two of these yield criterions can use in the transformation.

Mesoscale modeling of amorphous metals by shear transformation zone dynamics

International Nuclear Information System (INIS)

Homer, Eric R.; Schuh, Christopher A.

2009-01-01

A new mesoscale modeling technique for the thermo-mechanical behavior of metallic glasses is proposed. The modeling framework considers the shear transformation zone (STZ) as the fundamental unit of deformation, and coarse-grains an amorphous collection of atoms into an ensemble of STZs on a mesh. By employing finite element analysis and a kinetic Monte Carlo algorithm, the modeling technique is capable of simulating glass processing and deformation on time and length scales greater than those usually attainable by atomistic modeling. A thorough explanation of the framework is presented, along with a specific two-dimensional implementation for a model metallic glass. The model is shown to capture the basic behaviors of metallic glasses, including high-temperature homogeneous flow following the expected constitutive law, and low-temperature strain localization into shear bands. Details of the effects of processing and thermal history on the glass structure and properties are also discussed.

Examining shear processes during magma ascent

Science.gov (United States)

Kendrick, J. E.; Wallace, P. A.; Coats, R.; Lamur, A.; Lavallée, Y.

2017-12-01

Lava dome eruptions are prone to rapid shifts from effusive to explosive behaviour which reflects the rheology of magma. Magma rheology is governed by composition, porosity and crystal content, which during ascent evolves to yield a rock-like, viscous suspension in the upper conduit. Geophysical monitoring, laboratory experiments and detailed field studies offer the opportunity to explore the complexities associated with the ascent and eruption of such magmas, which rest at a pivotal position with regard to the glass transition, allowing them to either flow or fracture. Crystal interaction during flow results in strain-partitioning and shear-thinning behaviour of the suspension. In a conduit, such characteristics favour the formation of localised shear zones as strain is concentrated along conduit margins, where magma can rupture and heal in repetitive cycles. Sheared magmas often record a history of deformation in the form of: grain size reduction; anisotropic permeable fluid pathways; mineral reactions; injection features; recrystallisation; and magnetic anomalies, providing a signature of the repetitive earthquakes often observed during lava dome eruptions. The repetitive fracture of magma at ( fixed) depth in the conduit and the fault-like products exhumed at spine surfaces indicate that the last hundreds of meters of ascent may be controlled by frictional slip. Experiments on a low-to-high velocity rotary shear apparatus indicate that shear stress on a slip plane is highly velocity dependent, and here we examine how this influences magma ascent and its characteristic geophysical signals.

Dynamic compressive constitutive relation and shearing instability of metallic neodymium

International Nuclear Information System (INIS)

Wang Huanran; Cai Canyuan; Chen Danian; Ma Dongfang; Hou Yanjun; Wu Shanxing

2011-01-01

Highlights: → Dynamic constitutive relation of Nd was determined in first compression of SHPB. → Deformation of Nd in multi-compression of SHPB were recorded by high-speed camera. → Constitutive relation of Nd was adjusted in modeling large deformation of Nd. → Results of SDDM investigation of recovered Nd specimens showed shearing fracture. → Shearing instability of Nd was estimated with constitutive relation. - Abstract: Based on static tests on MTS and dynamic tests on split Hopkinson pressure bar (SHPB) during the first loading, this study determined the dynamic compressive constitutive relation of metallic Nd. Based on large deformations of metallic Nd specimens generated by the multi-compressive loadings during SHPB tests, and recorded by a high-speed camera, the results of numerical simulations for SHPB test processes were used to extend the determined constitutive relation from small strain to large strain. The shearing instability strain in dynamic compressive deformations of metallic Nd was estimated with the extended constitutive relation according to the criterion given by Batra and Wei, and was compared with the average strain of recovered specimens.

Shear crack formation and propagation in fiber reinforced cementitious composites (FRCC)

DEFF Research Database (Denmark)

Paegle, Ieva; Fischer, Gregor

2011-01-01

Knowledge of the mechanisms controlling crack formation, propagation and failure of FRCC under shear loading is currently limited. This paper presents a study that utilized photogrammetry to monitor the shear deformations of two FRCC materials and ordinary concrete (OC). Multiple shear cracks...... and strain hardening of both FRCC materials was observed under shear loading. The influence of fibers, fiber type, including polyvinyl alcohol (PVA) and polypropylene (PP) fibers, and shear crack angle were investigated. Based upon photogrammetric results, fundamental descriptions of shear crack opening...

Shear crack formation and propagation in fiber reinforced cementitious composites (FRCC)

DEFF Research Database (Denmark)

Paegle, Ieva; Fischer, Gregor

2012-01-01

Knowledge of the mechanisms controlling crack formation, propagation and failure of FRCC under shear loading is currently limited. This paper presents a study that utilized photogrammetry to monitor the shear deformations of two FRCC materials and ordinary concrete (OC). Multiple shear cracks...... and strain hardening of both FRCC materials was observed under shear loading. The influence of fibers, fiber type, including polyvinyl alcohol (PVA) and polypropylene (PP) fibers, and shear crack angle were investigated. Based upon photogrammetric results, fundamental descriptions of shear crack opening...

Migration of the deforming zone during seismic shear and implications for field observations, dynamic weakening, and the onset of melting

Science.gov (United States)

Platt, J. D.; Rice, J. R.

2013-12-01

Prior work in our group has shown how micron-scale strain rate localization can be explained using models for thermal pressurization and thermal decomposition in fluid-saturated gouge materials. Using parameters modeling a typical centroidal depth for a crustal seismogenic zone we predicted localized zone thicknesses in line with laboratory (Brantut et al., 2008; Kitajima et al., 2010) and field (Chester and Chester, 1998; Heermance et al., 2003; De Paola et al., 2008) observations. Further work has shown that the localized zone need not remain in a single location and may migrate across the gouge layer, in agreement with laboratory observations that show a thickening of the highly localized material with slip, and a distinct banded structure within the highly localized material (T. Mitchell, priv. comm.; Kitajima et al., 2010). We have identified two mechanisms that could cause migration. The first is a combination of thermal diffusion, hydraulic diffusion and thermal pressurization, which leads to the location of maximum pore pressure moving away from its initial position [Rice, 2006]. Since the maximum strain rate coincides with the maximum pore pressure, this causes the deforming zone to move across the gouge layer. The second mechanism is reactant depletion in a material undergoing thermal decomposition. Fluid pressurization and strain rate are slaved to the reaction, so as the reactant depletes the deforming zone will migrate towards fresh reactant. An additional symmetry breaking instability exists but is not discussed here. We have also explored how spatial variations in fault gouge properties may control the distribution of seismic shear. Since at seismic slip rates localization in a fluid-saturated material is controlled largely by pore pressure generation and hydraulic diffusion, regions that generate or trap pore pressures more efficiently will attract straining. Numerical simulations show that the deforming zone moves towards regions of low hydraulic

On the prediction of ductile fracture by void coalescence and strain localization

Science.gov (United States)

Luo, Tuo; Gao, Xiaosheng

2018-04-01

This paper presents a unit cell model based on the observation that ductile fracture occurs when plastic flow is localized in a band. The unit cell consists of three void containing material units stacked in the direction normal to the localization plane. Localization takes place in the middle material unit while the two outer units undergo elastic recovery after failure occurs. Thus a failure criterion is established as when the macroscopic effective strain of the outer material units reaches the maximum value. Analyses are conducted to demonstrate the effect of the voids existing outside the localization band. Comparisons of the present model with several previous models suggest that the present model is not only easy to implement in finite element analysis but also more suitable to robustly determine the failure strain. A series of unit cell analyses are conducted for various macroscopic stress triaxialities and Lode parameters. The analysis results confirm that for a fixed Lode parameter, the failure strain decreases exponentially with the stress triaxiality and for a given stress triaxiality, it increases as the stress state approaches the generalized tension and generalized compression. The analysis results also reveal the effect of the stress state on the deformed void shape within and near the localization band.

Development of a Shear Deformable Element Using the Absolute Nodal Coordinate Formulation

National Research Council Canada - National Science Library

Omar, Mohamed

2000-01-01

.... The effect of the shear deformation is accounted for without the need for introducing Timoshenko's shear coefficient By using the absolute coordinates, the nonlinear strain-displacement relationships...

Experimental study and FEM simulation of the simple shear test of cylindrical rods

Science.gov (United States)

Wirti, Pedro H. B.; Costa, André L. M.; Misiolek, Wojciech Z.; Valberg, Henry S.

2018-05-01

In the presented work an experimental simple shear device for cutting cylindrical rods was used to obtain force-displacement data for a low-carbon steel. In addition, and FEM 3D-simulation was applied to obtain internal shear stress and strain maps for this material. The experimental longitudinal grid patterns and force-displacement curve were compared with numerical simulation results. Many aspects of the elastic and plastic deformations were described. It was found that bending reduces the shear yield stress of the rod material. Shearing starts on top and bottom die-workpiece contact lines evolving in an arc-shaped area. Due to this geometry, stress concentrates on the surface of the rod until the level of damage reaches the critical value and the fracture starts here. The volume of material in the plastic zone subjected to shearing stress has a very complex shape and is function of a dimensionless geometrical parameter. Expressions to calculate the true shear stress τ and strain γ from the experimental force-displacement data were proposed. The equations' constants are determined by fitting the experimental curve with the stress τ and strain γ simulation point tracked data.

Modeling fracture in the context of a strain-limiting theory of elasticity: a single anti-plane shear crack

KAUST Repository

Rajagopal, K. R.

2011-01-06

This paper is the first part of an extended program to develop a theory of fracture in the context of strain-limiting theories of elasticity. This program exploits a novel approach to modeling the mechanical response of elastic, that is non-dissipative, materials through implicit constitutive relations. The particular class of models studied here can also be viewed as arising from an explicit theory in which the displacement gradient is specified to be a nonlinear function of stress. This modeling construct generalizes the classical Cauchy and Green theories of elasticity which are included as special cases. It was conjectured that special forms of these implicit theories that limit strains to physically realistic maximum levels even for arbitrarily large stresses would be ideal for modeling fracture by offering a modeling paradigm that avoids the crack-tip strain singularities characteristic of classical fracture theories. The simplest fracture setting in which to explore this conjecture is anti-plane shear. It is demonstrated herein that for a specific choice of strain-limiting elasticity theory, crack-tip strains do indeed remain bounded. Moreover, the theory predicts a bounded stress field in the neighborhood of a crack-tip and a cusp-shaped opening displacement. The results confirm the conjecture that use of a strain limiting explicit theory in which the displacement gradient is given as a function of stress for modeling the bulk constitutive behavior obviates the necessity of introducing ad hoc modeling constructs such as crack-tip cohesive or process zones in order to correct the unphysical stress and strain singularities predicted by classical linear elastic fracture mechanics. © 2011 Springer Science+Business Media B.V.

Laboratory studies on the effects of shear on fish: Final report

Energy Technology Data Exchange (ETDEWEB)

Neitzel, Duane A. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Richmond, M. C. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Dauble, D. D. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Mueller, R. P. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Moursund, R. A. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Abernethy, C. S. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Guensch, G. R. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Cada, G. F. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

2000-09-01

The overall objective of these studies was to specify an index describing the hydraulic force that fish experience when subjected to a shear environment. Fluid shear is a phenomenon that is important to fish. However, elevated levels of shear may result in strain rates that injure or kill fish. At hydroelectric generating facilities, concerns have been expressed that strain rates associated with passage through turbines, spillways, and fish bypass systems may adversely affect migrating fish. Development of fish-friendly hydroelectric turbines requires knowledge of the physical forces (injury mechanisms) that impact entrained fish and the fish’s tolerance to these forces. It requires up-front, pre-design specifications for the environmental conditions that occur within the turbine system; in other words, determining or assuming conditions known to injure fish will assist engineers in the design of a fish-friendly turbine system. To address the development of biological specifications, this experiment designed and built a test facility where juvenile fish could be subjected to a range of shear environments and quantified their biological response. The test data reported here provide quantified strain rates and the relationship of these forces to direct and indirect biological effects on fish. The study concludes that juvenile salmonids and American shad should survive shear environments where strain rates do not exceed 500 cm/s/cm at a Dy of 1.8 cm. Additional studies are planned with a sensor fish to better link hydraulic conditions found within the laboratory and field environments.

Magma shearing and friction in the volcanic conduit: A crystal constraint

Science.gov (United States)

Wallace, P. A.; Kendrick, J. E.; Henton De Angelis, S.; Ashworth, J. D.; Coats, R.; Miwa, T.; Mariani, E.; Lavallée, Y.

2017-12-01

Magma shearing and friction processes in the shallow volcanic conduit are typical manifestations of strain localisation, which in turn can have an influential role on magma ascent dynamics. The thermal consequences of such events could drive the destabilisation of magma and thus dictate the style of activity at the surface. Shear heating and fault friction are prime candidates for the generation of significant quantities of heat. Here we use a combination of field and experimental evidence to investigate how crystals can act as sensitive recorders of both physical and chemical processes occurring in the shallow volcanic conduit. Spine extrusion during the closing of the 1991-95 eruption at Unzen volcano, Japan, provided the unique opportunity to investigate marginal shear zone formation, which preserves a relic of the deformation during magma ascent. Our results show that crystals can effectively act as a deformation marker during magma ascent through the viscous-brittle transition by accommodating strain in the form of crystal plasticity before fracturing (comminution). Electron backscatter diffraction (EBSD) reveals up to 40° lattice distortion of biotite phenocrysts in zones of high shear, with negligible plasticity further away. Plagioclase microlites display a systematic plastic response to an increase in shear intensity, as recorded by an increase in lattice distortion towards the spine margin of up to 9°. This localisation of strain within the shear zone is also accompanied by the destabilisation of hydrous mineral phases (i.e. amphibole), compaction of pores (23-13% Φ), glass devitrification and magnetic anomalies. The narrow zone of disequilibrium textures suggests the likely effect of a thermal input due to strain localisation being the contributing factor. These observations are complimented by high-temperature high-velocity rotary shear experiments which simulate the deformation evolution during shear. Hence, understanding these shallow volcanic

Reynolds number scaling of straining motions in turbulence

Science.gov (United States)

Elsinga, Gerrit; Ishihara, T.; Goudar, M. V.; da Silva, C. B.; Hunt, J. C. R.

2017-11-01

Strain is an important fluid motion in turbulence as it is associated with the kinetic energy dissipation rate, vorticity stretching, and the dispersion of passive scalars. The present study investigates the scaling of the turbulent straining motions by evaluating the flow in the eigenframe of the local strain-rate tensor. The analysis is based on DNS of homogeneous isotropic turbulence covering a Reynolds number range Reλ = 34.6 - 1131. The resulting flow pattern reveals a shear layer containing tube-like vortices and a dissipation sheet, which both scale on the Kolmogorov length scale, η. The vorticity stretching motions scale on the Taylor length scale, while the flow outside the shear layer scales on the integral length scale. These scaling results are consistent with those in wall-bounded flow, which suggests a quantitative universality between the different flows. The overall coherence length of the vorticity is 120 η in all directions, which is considerably larger than the typical size of individual vortices, and reflects the importance of spatial organization at the small scales. Transitions in flow structure are identified at Reλ 45 and 250. Below these respective Reynolds numbers, the small-scale motions and the vorticity stretching motions appear underdeveloped.

Predicting Shear Transformation Events in Metallic Glasses

Science.gov (United States)

Xu, Bin; Falk, Michael L.; Li, J. F.; Kong, L. T.

2018-03-01

Shear transformation is the elementary process for plastic deformation of metallic glasses, the prediction of the occurrence of the shear transformation events is therefore of vital importance to understand the mechanical behavior of metallic glasses. In this Letter, from the view of the potential energy landscape, we find that the protocol-dependent behavior of shear transformation is governed by the stress gradient along its minimum energy path and we propose a framework as well as an atomistic approach to predict the triggering strains, locations, and structural transformations of the shear transformation events under different shear protocols in metallic glasses. Verification with a model Cu64 Zr36 metallic glass reveals that the prediction agrees well with athermal quasistatic shear simulations. The proposed framework is believed to provide an important tool for developing a quantitative understanding of the deformation processes that control mechanical behavior of metallic glasses.

Nested separatrices in simple shear flows: the effect of localized disturbances on stagnation lines

OpenAIRE

Wilson, M.C.T.; Gaskell, P.H.; Savage, M.D.

2005-01-01

The effects of localized two-dimensional disturbances on the structure of shear flows featuring a stagnation line are investigated. A simple superposition of a planar Couette flow and Moffatt's [J. Fluid Mech. 18, 1--18 (1964)] streamfunction for the decay of a disturbance between infinite stationary parallel plates shows that in general the stagnation line is replaced by a chain of alternating elliptic and hyperbolic stagnation points with a separation equal to 2.78 times the half-gap betwee...

Shear behavior of reinforced Engineered Cementitious Composites (ECC) beams

DEFF Research Database (Denmark)

Paegle, Ieva; Fischer, Gregor

2010-01-01

This paper describes an experimental investigation of the shear behavior of beams consisting of steel reinforced Engineered Cementitious Composites (ECC). Based on the strain hardening and multiple cracking behavior of ECC, this study investigates the extent to which ECC can improve the shear...... capacity of beams loaded primarily in shear and if ECC can partially or fully replace the conventional transverse steel reinforcement in beams. However, there is a lack of understanding of how the fibers affect the shear carrying capacity and deformation behavior of structural members if used either...

An integrated approach to model strain localization bands in magnesium alloys

Science.gov (United States)

Baxevanakis, K. P.; Mo, C.; Cabal, M.; Kontsos, A.

2018-02-01

Strain localization bands (SLBs) that appear at early stages of deformation of magnesium alloys have been recently associated with heterogeneous activation of deformation twinning. Experimental evidence has demonstrated that such "Lüders-type" band formations dominate the overall mechanical behavior of these alloys resulting in sigmoidal type stress-strain curves with a distinct plateau followed by pronounced anisotropic hardening. To evaluate the role of SLB formation on the local and global mechanical behavior of magnesium alloys, an integrated experimental/computational approach is presented. The computational part is developed based on custom subroutines implemented in a finite element method that combine a plasticity model with a stiffness degradation approach. Specific inputs from the characterization and testing measurements to the computational approach are discussed while the numerical results are validated against such available experimental information, confirming the existence of load drops and the intensification of strain accumulation at the time of SLB initiation.

Simple shearing flow of dry soap foams with tetrahedrally close-packed structure

Energy Technology Data Exchange (ETDEWEB)

Reinelt, Douglas A. [Department of Mathematics, Southern Methodist University, Dallas, Texas 75275-0156 (United States); Kraynik, Andrew M. [Engineering Sciences Center, Sandia National Laboratories, Albuquerque, New Mexico 87185-0834 (United States)

2000-05-01

The microrheology of dry soap foams subjected to quasistatic, simple shearing flow is analyzed. Two different monodisperse foams with tetrahedrally close-packed (TCP) structure are examined: Weaire-Phelan (A15) and Friauf-Laves (C15). The elastic-plastic response is evaluated by using the Surface Evolver to calculate foam structures that minimize total surface area at each value of strain. The foam geometry and macroscopic stress are piecewise continuous functions of strain. The stress scales as T/V{sup 1/3}, where T is surface tension and V is cell volume. Each discontinuity corresponds to large changes in foam geometry and topology that restore equilibrium to unstable configurations that violate Plateau's laws. The instabilities occur when the length of an edge on a polyhedral foam cell vanishes. The length can tend to zero smoothly or abruptly with strain. The abrupt case occurs when a small increase in strain changes the energy profile in the neighborhood of a foam structure from a local minimum to a saddle point, which can lead to symmetry-breaking bifurcations. In general, the new structure associated with each stable solution branch results from an avalanche of local topology changes called T1 transitions. Each T1 cascade produces different cell neighbors, reduces surface energy, and provides an irreversible, film-level mechanism for plastic yield behavior. Stress-strain curves and average stresses are evaluated by examining foam orientations that admit strain-periodic behavior. For some orientations, the deformation cycle includes Kelvin cells instead of the original TCP structure; but the foam does not remain perfectly ordered. Bifurcations during subsequent T1 cascades lead to disorder and can even cause strain localization. (c) 2000 Society of Rheology.

On Necking, Fracture and Localization of Plastic Flow in Austenitic Stainless Steel Sheets

International Nuclear Information System (INIS)

Korhonen, A. S.; Manninen, T.; Kanervo, K.

2007-01-01

The forming limits of austenitic stainless steel sheets were studied in this work. It was found that the observed limit of straining in stretch forming, when both of the principal stresses are positive, is not set by localized necking, but instead by inclined shearing fracture in the through thickness direction. It appears that the forming limits of austenitic stainless steels may be predicted fairly well by using the classical localized and diffuse necking criteria developed by Hill. The strain path-dependence may be accounted for by integrating the effective strain along the strain path. The fracture criteria of Rice and Tracey and Cockcroft, Latham and Oh were also studied. The results were in qualitative agreement with the experimental observations. Recent experiments with high-velocity electrohydraulic forming of austenitic stainless steels revealed localized necks in stretch formed parts, which are not commonly observed in conventionally formed sheet metal parts

The electronic origin of shear-induced direct to indirect gap transition and anisotropy diminution in phosphorene.

Science.gov (United States)

Sa, Baisheng; Li, Yan-Ling; Sun, Zhimei; Qi, Jingshan; Wen, Cuilian; Wu, Bo

2015-05-29

Artificial monolayer black phosphorus, so-called phosphorene, has attracted global interest with its distinguished anisotropic, optoelectronic, and electronic properties. Here, we unraveled the shear-induced direct-to-indirect gap transition and anisotropy diminution in phosphorene based on first-principles calculations. Lattice dynamic analysis demonstrates that phosphorene can sustain up to 10% applied shear strain. The bandgap of phosphorene experiences a direct-to- indirect transition when 5% shear strain is applied. The electronic origin of the direct-to-indirect gap transition from 1.54 eV at ambient conditions to 1.22 eV at 10% shear strain for phosphorene is explored. In addition, the anisotropy diminution in phosphorene is discussed by calculating the maximum sound velocities, effective mass, and decomposed charge density, which signals the undesired shear-induced direct-to-indirect gap transition in applications of phosphorene for electronics and optoelectronics. On the other hand, the shear-induced electronic anisotropy properties suggest that phosphorene can be applied as the switcher in nanoelectronic applications.

Shear-driven dynamic clusters in a colloidal glass

Science.gov (United States)

Eisenmann, Christoph; Kim, Chanjoong; Mattsson, Johan; Weitz, David

2007-03-01

We investigate the effect of shear applied to a colloidal glass on a microscopic level using a shear device that can be mounted on top of a confocal microscope. We find that the glass yields at a critical strain of about 10%, independently of the shear rate. Surprisingly, the yielding is accompanied by an increase of cooperative particle movements and a formation of dynamic clusters which is in contrast to the normal glass transition where one typically finds heterogeneity increasing whilst moving towards the glass transition.

Shear-induced partial translational ordering of a colloidal solid

Science.gov (United States)

Ackerson, B. J.; Clark, N. A.

1984-08-01

Highly charged submicrometer plastic spheres suspended in water at low ionic strength will order spontaneously into bcc crystals or polycrystals. A simple linear shear orients and disorders these crystals by forcing (110) planes to stack normal to the shear gradient and to slide relative to each other with a direction parallel to the solvent flow. In this paper we analyze in detail the disordering and flow processes occurring beyond the intrinsic elastic limit of the bcc crystal. We are led to a model in which the flow of a colloidal crystal is interpreted as a fundamentally different process from that found in atomic crystals. In the colloidal crystal the coupling of particle motion to the background fluid forces a homogeneous flow, where every layer is in motion relative to its neighboring layers. In contrast, the plastic flow in an atomic solid is defect mediated flow. At the lowest applied stress, the local bcc order in the colloidal crystal exhibits shear strains both parallel and perpendicular to the direction of the applied stress. The magnitude of these deformations is estimated using the configurational energy for bcc and distorted bcc crystals, assuming a screened Coulomb pair interaction between colloidal particles. As the applied stress is increased, the intrinsic elastic limit of the crystal is exceeded and the crystal begins to flow with adjacent layers executing an oscillatory path governed by the balance of viscous and screened Coulomb forces. The path takes the structure from the bcc1 and bcc2 twins observed at zero shear to a distorted two-dimensional hcp structure at moderate shear rates, with a loss of interlayer registration as the shear is increased. This theoretical model is consistent with other experimental observations, as well.

Shear Strength of Remoulding Clay Samples Using Different Methods of Moulding

Science.gov (United States)

Norhaliza, W.; Ismail, B.; Azhar, A. T. S.; Nurul, N. J.

2016-07-01

Shear strength for clay soil was required to determine the soil stability. Clay was known as a soil with complex natural formations and very difficult to obtain undisturbed samples at the site. The aim of this paper was to determine the unconfined shear strength of remoulded clay on different methods in moulding samples which were proctor compaction, hand operated soil compacter and miniature mould methods. All the samples were remoulded with the same optimum moisture content (OMC) and density that were 18% and 1880 kg/m3 respectively. The unconfined shear strength results of remoulding clay soils for proctor compaction method was 289.56kPa with the strain 4.8%, hand operated method was 261.66kPa with the strain 4.4% and miniature mould method was 247.52kPa with the strain 3.9%. Based on the proctor compaction method, the reduction percentage of unconfined shear strength of remoulded clay soil of hand operated method was 9.66%, and for miniature mould method was 14.52%. Thus, because there was no significant difference of reduction percentage of unconfined shear strength between three different methods, so it can be concluded that remoulding clay by hand operated method and miniature mould method were accepted and suggested to perform remoulding clay samples by other future researcher. However for comparison, the hand operated method was more suitable to form remoulded clay sample in term of easiness, saving time and less energy for unconfined shear strength determination purposes.

The Mercier Criterion in Reversed Shear Tokamak Plasmas

International Nuclear Information System (INIS)

Kessel, C.; Chance, M.S.; Jardin, S.C.

1999-01-01

A recent numerical study has found that, contrary to conventional theoretical and experimental expectations, reversed shear plasmas are unstable primarily because the term proportional to the shear in the Mercier criterion is destabilizing. In the present study, the role of the magnetic shear, both local and global, is examined for various tokamak configurations with monotonic and non-monotonic safety factor profiles. The enhancement of the local shear due to the outward shift of the magnetic axis suggests that the latter are less susceptible to interchanges. Furthermore, by regrouping the terms in the criterion, the V'' term when differentiated instead with respect to the toroidal flux, is shown to absorb the dominant shear term. No Mercier instability is found for similar profiles as in the previous study

A nanoindentation investigation of local strain rate sensitivity in dual-phase Ti alloys

Energy Technology Data Exchange (ETDEWEB)

Jun, Tea-Sung, E-mail: t.jun@imperial.ac.uk [Department of Materials, Royal School of Mines, Imperial College London, London, SW7 2AZ (United Kingdom); Armstrong, David E.J. [Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH (United Kingdom); Britton, T. Benjamin [Department of Materials, Royal School of Mines, Imperial College London, London, SW7 2AZ (United Kingdom)

2016-07-05

Using nanoindentation we have investigated the local strain rate sensitivity in dual-phase Ti alloys, Ti–6Al–2Sn–4Zr-xMo (x = 2 and 6), as strain rate sensitivity could be a potential factor causing cold dwell fatigue. Electron backscatter diffraction (EBSD) was used to select hard and soft grain orientations within each of the alloys. Nanoindentation based tests using the continuous stiffness measurement (CSM) method were performed with variable strain rates, on the order of 10{sup −1} to 10{sup −3}s{sup −1}. Local strain rate sensitivity is determined using a power law linking equivalent flow stress and equivalent plastic strain rate. Analysis of residual impressions using both a scanning electron microscope (SEM) and a focused ion beam (FIB) reveals local deformation around the indents and shows that nanoindentation tested structures containing both α and β phases within individual colonies. This indicates that the indentation results are derived from averaged α/β properties. The results show that a trend of local rate sensitivity in Ti6242 and Ti6246 is strikingly different; as similar rate sensitivities are found in Ti6246 regardless of grain orientation, whilst a grain orientation dependence is observed in Ti6242. These findings are important for understanding dwell fatigue deformation modes, and the methodology demonstrated can be used for screening new alloy designs and microstructures. - Highlights: • Nanoindentation-based CSM tests were performed on dual-phase Ti alloys. • EBSD was effectively used to select target grains within isolated morphologies. • A trend of local rate sensitivity in Ti6242 and Ti6246 is strikingly different. • A significant grain orientation dependent rate sensitivity is observed in Ti6242. • Similar rate sensitivities are found in Ti6246 regardless of grain orientation.

Shear crack formation and propagation in reinforced Engineered Cementitious Composites

DEFF Research Database (Denmark)

Paegle, Ieva; Fischer, Gregor

2011-01-01

capacity of beams loaded primarily in shear. The experimental program consists of ECC with short randomly distributed polyvinyl alcohol (PVA) fiber beams with different stirrup arrangements and conventional reinforced concrete (R/C) counterparts for comparison. The shear crack formation mechanism of ECC......This paper describes an experimental investigation of the shear behaviour of beams consisting of steel reinforced Engineered Cementitious Composites (R/ECC). Based on the strain hardening and multiple cracking behaviour of ECC, this study investigates the extent to which ECC influences the shear...

Evolution of strain localization in variable-width three-dimensional unsaturated laboratory-scale cut slopes

Science.gov (United States)

Morse, Michael S.; Lu, Ning; Wayllace, Alexandra; Godt, Jonathan W.

2017-01-01

To experimentally validate a recently developed theory for predicting the stability of cut slopes under unsaturated conditions, the authors measured increasing strain localization in unsaturated slope cuts prior to abrupt failure. Cut slope width and moisture content were controlled and varied in a laboratory, and a sliding door that extended the height of the free face of the slope was lowered until the cut slope failed. A particle image velocimetry tool was used to quantify soil displacement in the x-y">x-y (horizontal) and x-z">x-z (vertical) planes, and strain was calculated from the displacement. Areas of maximum strain localization prior to failure were shown to coincide with the location of the eventual failure plane. Experimental failure heights agreed with the recently developed stability theory for unsaturated cut slopes (within 14.3% relative error) for a range of saturation and cut slope widths. A theoretical threshold for sidewall influence on cut slope failures was also proposed to quantify the relationship between normalized sidewall width and critical height. The proposed relationship was consistent with the cut slope experiment results, and is intended for consideration in future geotechnical experiment design. The experimental data of evolution of strain localization presented herein provide a physical basis from which future numerical models of strain localization can be validated.

Predictions and Experimental Microstructural Characterization of High Strain Rate Failure Modes in Layered Aluminum Composites

Science.gov (United States)

Khanikar, Prasenjit

Different aluminum alloys can be combined, as composites, for tailored dynamic applications. Most investigations pertaining to metallic alloy layered composites, however, have been based on quasi-static approaches. The dynamic failure of layered metallic composites, therefore, needs to be characterized in terms of strength, toughness, and fracture response. A dislocation-density based crystalline plasticity formulation, finite-element techniques, rational crystallographic orientation relations and a new fracture methodology were used to predict the failure modes associated with the high strain rate behavior of aluminum layered composites. Two alloy layers, a high strength alloy, aluminum 2195, and an aluminum alloy 2139, with high toughness, were modeled with representative microstructures that included precipitates, dispersed particles, and different grain boundary (GB) distributions. The new fracture methodology, based on an overlap method and phantom nodes, is used with a fracture criteria specialized for fracture on different cleavage planes. One of the objectives of this investigation, therefore, was to determine the optimal arrangements of the 2139 and 2195 aluminum alloys for a metallic layered composite that would combine strength, toughness and fracture resistance for high strain-rate applications. Different layer arrangements were investigated for high strain-rate applications, and the optimal arrangement was with the high toughness 2139 layer on the bottom, which provided extensive shear strain localization, and the high strength 2195 layer on the top for high strength resistance. The layer thickness of the bottom high toughness layer also affected the bending behavior of the roll-boned interface and the potential delamination of the layers. Shear strain localization, dynamic cracking and delamination were the mutually competing failure mechanisms for the layered metallic composite, and control of these failure modes can be optimized for high strain

Special Features of Strain Localization and Nanodipoles of Partial Disclinations in the Region of Elastic Distortions

Science.gov (United States)

Tyumentsev, A. N.; Ditenberg, I. A.; Sukhanov, I. I.

2018-02-01

In the zones of strain localization in the region of elastic distortions and nanodipoles of partial disclinations representing the defects of elastically deformed medium, a theoretical analysis of the elastically stressed state and the energy of these defects, including the cases of their transformation into more complex ensembles of interrelated disclinations, is performed. Using the analytical results, the mechanisms of strain localization are discussed in the stages of nucleation and propagation of the bands of elastic and plastic strain localization formed in these zones (including the cases of nanocrystalline structure formation).

Micromechanics of deformation of metallic-glass-matrix composites from in situ synchrotron strain measurements and finite element modeling

International Nuclear Information System (INIS)

Ott, R.T.; Sansoz, F.; Molinari, J.F.; Almer, J.; Ramesh, K.T.; Hufunagel, T.C.

2005-01-01

In situ X-ray scattering and finite element modeling (FEM) were used to examine the micromechanics of deformation of in situ formed metallic-glass-matrix composites consisting of Ta-rich particles dispersed in an amorphous matrix. The strain measurements show that under uniaxial compression the second-phase particles yield at an applied stress of approx. 325 MPa. After yielding, the particles do not strain harden significantly; we show that this is due to an increasingly hydrostatic stress state arising from the lateral constraint on deformation of the particles imposed by the elastic matrix. Shear band initiation in the matrix is not due to the difference in elastic properties between the matrix and the particles. Rather, the development of a plastic misfit strain causes stress concentrations around the particles, resulting in localized yielding of the matrix by shear band formation at an applied stress of approx. 1450 MPa, considerably lower than the macroscopic yield stress of the composite (approx. 1725 MPa). Shear bands do not propagate at the lower stress because the yield criterion of the matrix is only satisfied in the region immediately around the particles. At the higher stresses, the yield criterion is satisfied in large regions of the matrix, allowing extensive shear band propagation and significant macroscopic plastic deformation. However, the presence of the particles makes the stress state highly inhomogeneous, which may partially explain why fracture is suppressed in the composite, allowing the development of large plastic strains

Effect of Shear Applied During a Pharmaceutical Process on Near Infrared Spectra.

Science.gov (United States)

Hernández, Eduardo; Pawar, Pallavi; Rodriguez, Sandra; Lysenko, Sergiy; Muzzio, Fernando J; Romañach, Rodolfo J

2016-03-01

This study describes changes observed in the near-infrared (NIR) diffuse reflectance (DR) spectra of pharmaceutical tablets after these tablets were subjected to different levels of strain (exposure to shear) during the mixing process. Powder shearing is important in the mixing of powders that are cohesive. Shear stress is created in a system by moving one surface over another causing displacements in the direction of the moving surface and is part of the mixing dynamics of particulates in many industries including the pharmaceutical industry. In continuous mixing, shear strain is developed within the process when powder particles are in constant movement and can affect the quality attributes of the final product such as dissolution. These changes in the NIR spectra could affect results obtained from NIR calibration models. The aim of the study was to understand changes in the NIR diffuse reflectance spectra that can be associated with different levels of strain developed during blend shearing of laboratory samples. Shear was applied using a Couette cell and tablets were produced using a tablet press emulator. Tablets with different shear levels were measured using NIR spectroscopy in the diffuse reflectance mode. The NIR spectra were baseline corrected to maintain the scattering effect associated with the physical properties of the tablet surface. Principal component analysis was used to establish the principal sources of variation within the samples. The angular dependence of elastic light scattering shows that the shear treatment reduces the size of particles and produces their uniform and highly isotropic distribution. Tablet compaction further reduces the diffuse component of scattering due to realignment of particles. © The Author(s) 2016.

Direct Strain and Slope and Slope Measurement Using 2D DSPSI

International Nuclear Information System (INIS)

Dandach, W.; Molimard, J.; Picart, P.

2011-01-01

Large variety of optical full-field measurement techniques are being developed and applied to solve mechanical problems. Since each technique possesses its own merits, it is important to know the capabilities and limitations of such techniques. Among these optical full-field methods, interferometry techniques take an important place. They are based on illumination with coherent light (laser). In shearing interferometry the difference of the out of-plane displacement in two neighboring object points is directly measured. Since object displacement does not result in interferometry fringes, the method is suited for localization of strain concentrations and is indeed used in industry for this purpose. DSPSI possesses the advantage over conventional out-of-plane displacement-sensitive interferometry, that only a single difference of the unwrapped phase map is required to obtain flexural strains, thereby relieving problems with noise and reduction in the field of view. A first work in this domain (DSPSI) [1] was made in 1973, later recent studies emerged to provide a quantitative system of measurements [2]. This work aims to present the results of strain and slope measurements using digital speckle pattern shearing interferometry (DSPSI). (author)

Microstructural Damage During High-Strain Torsion Experiments on Calcite-Anhydrite Aggregates

Science.gov (United States)

Cross, A. J.; Skemer, P. A.

2016-12-01

Ductile shear zones play a critical role in localising deformation in the Earth's crust and mantle. Severe grain size reduction - a ubiquitous feature of natural mylonites - is commonly thought to cause strain weakening via a transition to grain size sensitive deformation mechanisms. Although grain size reduction is modulated by grain growth in single-phase aggregates, grain boundary pinning in well-mixed poly-phase composites can inhibit grain growth, leading to microstructural `damage' which is likely a critical element of strain localization in the lithosphere. While dynamic recrystallization has been widely explored in rock mechanics and materials science, the mechanisms behind phase-mixing remain poorly understood. In this contribution we present results from high-strain, deformation experiments on calcite-anhydrite composites. Experiments were conducted in torsion at T = 500-700°C and P 1.5 GPa, using the new Large Volume Torsion (LVT) solid-medium apparatus, to shear strains of 0.5-30. As shear strain increases, progressive thinning and necking of initially large (≤ 1 mm) calcite domains is observed, resulting in an increase in the proportion of interphase boundaries. Grain-size is negatively correlated with the fraction of interphase boundaries, such that calcite grains in well-mixed regions are significantly smaller than those in single-phase domains. Crucially, progressive deformation leads to a reduction in grain-size beyond the lower limit established by the grain size piezometer for mono-phase calcite, implying microstructural damage. These data therefore demonstrate continued microstructural evolution in two-phase composites that is not possible in single-phase aggregates. These observations mark a new `geometric' mechanism for phase mixing, complementing previous models for phase mixing involving chemical reactions, material diffusion, and/or grain boundary sliding.

CFD simulation of estimating critical shear stress for cleaning flat ...

Indian Academy of Sciences (India)

Sumit Kawale

2017-11-22

Nov 22, 2017 ... Jet impingement; wall shear stress; cleaning of flat plate; turbulence model; critical shear stress; ... On comparing the theoretical predictions with wall shear ... distance and Reynolds number on peak value of local shear stress ...

Strain-accelerated dynamics of soft colloidal glasses

KAUST Repository

Agarwal, Praveen

2011-04-11

We have investigated strain-accelerated dynamics of soft glasses theoretically and experimentally. Mechanical rheology measurements performed on a variety of systems reveal evidence for the speeding-up of relaxation at modest shear strains in both step and oscillatory shear flows. Using the soft glassy rheology (SGR) model framework, we show that the observed behavior is a fundamental, but heretofore unexplored attribute of soft glasses. © 2011 American Physical Society.

Evaluation of stress distribution due to shearing in non-oriented electrical steel by using synchrotron radiation

Directory of Open Access Journals (Sweden)

Yoshiaki Zaizen

2016-05-01

Full Text Available The influence of the shearing process on the iron loss of non-oriented electrical steels with grain sizes of 10 μm-150 μm was investigated. The deterioration ratio of iron loss was clearly smaller in sample with small grain sizes. The droop height, reflecting the amount of plastic deformation, displayed a good relationship with the deterioration of iron loss under the effect of the material grain size. To clarify the strain distribution around the sheared edge, the elastic strain in a sheet sample with the thickness of 0.30 mm and grain size of 10 μm was evaluated by using synchrotron radiation. The width of the region of elastic strain due to shearing was two or three times of the material thickness. The results of the plastic strain distribution obtained by the measurements were then used to estimate the iron loss deterioration rate in 5 mm width sheared samples. The estimated loss deteriotation coincided with the actual measured iron loss.

Evaluation of stress distribution due to shearing in non-oriented electrical steel by using synchrotron radiation

Energy Technology Data Exchange (ETDEWEB)

Zaizen, Yoshiaki, E-mail: y-zaizen@jfe-steel.co.jp; Omura, Takeshi; Senda, Kunihiro [Steel Research Laboratory, JFE Steel Corporation, Kawasakidori 1,Mizushima, Kurashiki,712-8511 (Japan); Fukumura, Masaru [Steel Research Laboratory, JFE Steel Corporation, Kawasaki, Kanagawa 210-0855 (Japan); Toda, Hiroaki [Steel Business Planning Dept, JFE Steel Corporation, Tokyo 100-0011 (Japan)

2016-05-15

The influence of the shearing process on the iron loss of non-oriented electrical steels with grain sizes of 10 μm-150 μm was investigated. The deterioration ratio of iron loss was clearly smaller in sample with small grain sizes. The droop height, reflecting the amount of plastic deformation, displayed a good relationship with the deterioration of iron loss under the effect of the material grain size. To clarify the strain distribution around the sheared edge, the elastic strain in a sheet sample with the thickness of 0.30 mm and grain size of 10 μm was evaluated by using synchrotron radiation. The width of the region of elastic strain due to shearing was two or three times of the material thickness. The results of the plastic strain distribution obtained by the measurements were then used to estimate the iron loss deterioration rate in 5 mm width sheared samples. The estimated loss deteriotation coincided with the actual measured iron loss.

On the self-organizing process of large scale shear flows

Energy Technology Data Exchange (ETDEWEB)

Newton, Andrew P. L. [Department of Applied Maths, University of Sheffield, Sheffield, Yorkshire S3 7RH (United Kingdom); Kim, Eun-jin [School of Mathematics and Statistics, University of Sheffield, Sheffield, Yorkshire S3 7RH (United Kingdom); Liu, Han-Li [High Altitude Observatory, National Centre for Atmospheric Research, P. O. BOX 3000, Boulder, Colorado 80303-3000 (United States)

2013-09-15

Self organization is invoked as a paradigm to explore the processes governing the evolution of shear flows. By examining the probability density function (PDF) of the local flow gradient (shear), we show that shear flows reach a quasi-equilibrium state as its growth of shear is balanced by shear relaxation. Specifically, the PDFs of the local shear are calculated numerically and analytically in reduced 1D and 0D models, where the PDFs are shown to converge to a bimodal distribution in the case of finite correlated temporal forcing. This bimodal PDF is then shown to be reproduced in nonlinear simulation of 2D hydrodynamic turbulence. Furthermore, the bimodal PDF is demonstrated to result from a self-organizing shear flow with linear profile. Similar bimodal structure and linear profile of the shear flow are observed in gulf stream, suggesting self-organization.

Oceanic Loading and Local Distortions at the Baksan, Russia, and Gran Sasso, Italy, Strain Stations

Science.gov (United States)

Milyukov, V. K.; Amoruso, A.; Crescentini, L.; Mironov, A. P.; Myasnikov, A. V.; Lagutkina, A. V.

2018-03-01

Reliable use of strain data in geophysical studies requires their preliminary correction for ocean loading and various local distortions. These effects, in turn, can be estimated from the tidal records which are contributed by solid and oceanic loading. In this work, we estimate the oceanic tidal loading at two European strain stations (Baksan, Russia, and Gran Sasso, Italy) by analyzing the results obtained with the different Earth and ocean models. The influence of local distortions on the strain measurements at the two stations is estimated.

MM98.57 Quantification of Combined Strain Paths

DEFF Research Database (Denmark)

Nielsen, Morten Sturgård; Wanheim, Tarras

1998-01-01

this curve into useful scalar relations from experimental data.The strain history for plane strain when assuming volume constancy may be plotted in a shear strain, normal strain diagram, which has the property of showing both the rotation of principal deformation axes during the deformation and the amount...... is to describe the total strain history as a curve in the 6-dimensional shear strain, normal strain space. In order to be able to use these experimental data for calculation, the development of this strain curve must be transformed into a set of scalar relations that may be used for predicting the yield surface...... at a given point in a new strain history. A simple example of this concept is to take the length of the strain curve as describing scalar relation: E.g. to use the equivalent strain as parameter for describing the yield stress. This paper focuses on the strain curve concept and the possibilities to convert...

A fundamental discussion of what triggers localized deformation in geological materials

Science.gov (United States)

Peters, Max; Paesold, Martin; Poulet, Thomas; Herwegh, Marco; Regenauer-Lieb, Klaus; Veveakis, Manolis

2015-04-01

Discontinuous or localized structures are often marked by the transition from a homogeneously deforming into a highly localized mode. This transition has extensively been described in ductile shear zones, folding and pinch-and-swell boudinage, in natural examples, rock deformation experiments and numerical simulations, at various scales. It is conventionally assumed that ductile instabilities, which act as triggers for localized deformation, exclusively arise from structural heterogeneities, i.e. geometric interactions or material imperfections. However, Hansen et al. (2012) concluded from recent laboratory experiments that localized deformation might arise out of steady-state conditions, where the size of initial perturbations was either insufficiently large to trigger localization, or these heterogeneities were simply negligible at the scale of observation. We therefore propose the existence of a principal localization phenomenon, which is based on the material-specific rate-dependency of deformation at elevated temperatures. The concept of strain localization out of a mechanical steady state in a homogeneous material at a critical material parameter and/or deformation rate has previously been discussed for engineering materials (Gruntfest, 1963) and frictional faults (Veveakis et al., 2010). We expand this theory to visco-plastic carbonate rocks, considering deformation conditions and mechanisms encountered in naturally deformed rocks. In the numerical simulation, we implement a grain-size evolution based on the Paleowattmeter scaling relationship of Austin & Evans (2007), which takes both grain size sensitive (diffusion) and insensitive (dislocation) creep combined with grain growth into account (Herwegh et al., 2014). Based on constant strain rate simulations carried out under isothermal boundary conditions, we explore the parameter space in order to obtain the criteria for localization. We determine the criteria for the onset of localization, i.e. the

Effect of Attachment Type on Denture Strain in Maxillary Implant Overdentures: Part 1. Overdenture with Palate.

Science.gov (United States)

Takahashi, Toshihito; Gonda, Tomoya; Maeda, Yoshinobu

This study examined the effects of attachments on strain in maxillary implant overdentures supported by two or four implants. A maxillary edentulous model with implants inserted into anterior, premolar, and molar areas was fabricated, and three types of unsplinted attachments-ball, locator, and magnet-were set on the implants distributed under various conditions. Maxillary experimental dentures were fabricated, and two strain gauges were attached at the anterior midline on the labial and palatal sides. A vertical occlusal load of 98 N was applied and shear strain of the dentures was measured. On both sides, magnet attachments resulted in the lowest shear strain, while ball attachments resulted in the highest shear strain under most conditions. However, differences in shear strain among the three attachment types were not significant when supported by four implants, especially molar implants. Shear strain of the maxillary implant overdenture was lowest when using magnet attachments. Magnet attachments mounted on four implants are recommended to prevent denture complications when using maxillary implant overdentures.

Elliptical posts allow for detailed control of non-equibiaxial straining of cell cultures

DEFF Research Database (Denmark)

Olesen, Christian Gammelgaard; Pennisi, Cristian Pablo; de Zee, Mark

2013-01-01

tissue cells in vivo are subjected to a range of mechanical deformations including shear strain caused by activities of daily living. Shear strains are suspected to play an important role in tissue necrosis. Method The Flexcell system was redesigned using a finite element model in order to obtain large...... areas of the membrane in a controlled, uniform non-equibiaxial strain state. Results The redesign was manufactured and the resulting strains were experimentally validated by means of image analysis methods. The results showed that the system could be used for experiments varying the shear strain....... Conclusion The result allows scientists and experimentalists to apply detailed control of the strain tensor applied to tissue samples in two dimensions....

Comparative Laboratory and Numerical Simulations of Shearing Granular Fault Gouge: Micromechanical Processes

Science.gov (United States)

Morgan, J. K.; Marone, C. J.; Guo, Y.; Anthony, J. L.; Knuth, M. W.

2004-12-01

Laboratory studies of granular shear zones have provided significant insight into fault zone processes and the mechanics of earthquakes. The micromechanisms of granular deformation are more difficult to ascertain, but have been hypothesized based on known variations in boundary conditions, particle properties and geometries, and mechanical behavior. Numerical simulations using particle dynamics methods (PDM) can offer unique views into deforming granular shear zones, revealing the precise details of granular microstructures, particle interactions, and packings, which can be correlated with macroscopic mechanical behavior. Here, we describe a collaborative program of comparative laboratory and numerical experiments of granular shear using idealized materials, i.e., glass beads, glass rods or pasta, and angular sand. Both sets of experiments are carried out under similar initial and boundary conditions in a non-fracturing stress regime. Phenomenologically, the results of the two sets of experiments are very similar. Peak friction values vary as a function of particle dimensionality (1-D vs. 2-D vs. 3-D), particle angularity, particle size and size distributions, boundary roughness, and shear zone thickness. Fluctuations in shear strength during an experiment, i.e., stick-slip events, can be correlated with distinct changes in the nature, geometries, and durability of grain bridges that support the shear zone walls. Inclined grain bridges are observed to form, and to support increasing loads, during gradual increases in assemblage strength. Collapse of an individual grain bridge leads to distinct localization of strain, generating a rapidly propagating shear surface that cuts across multiple grain bridges, accounting for the sudden drop in strength. The distribution of particle sizes within an assemblage, along with boundary roughness and its periodicity, influence the rate of formation and dissipation of grain bridges, thereby controlling friction variations during

High Resolution Shear Profile Measurements in Entangled Polymers

KAUST Repository

Hayes, Keesha A.

2008-11-17

We use confocal microscopy and particle image velocimetry to visualize motion of 250-300 nm. fluorescent tracer particles in entangled polymers subject to a rectilinear shear flow. Our results show linear velocity profiles in polymer solutions spanning a wide range of molecular weights and number of entanglements (8≤Z≤56), but reveal large differences between the imposed and measured shear rates. These findings disagree with recent reports that shear banding is a characteristic flow response of entangled polymers, and instead point to interfacial slip as an important source of strain loss. © 2008 The American Physical Society.

Shear modulation experiments with ECCD on TCV

International Nuclear Information System (INIS)

Cirant, S.; Alberti, S.; Gandini, F.; Behn, R.; Goodman, T.P.; Nikkola, P.

2006-01-01

Anomalous electron transport is determined by turbulence, which in turn is affected by magnetic shear. A novel application of electron cyclotron current drive (ECCD), aiming at localized shear modulation, has been applied on the TCV tokamak for experiments on shear-dependent electron transport. Pairs of EC beams, absorbed at the same radius, with one oriented for co- and the other for counter-injection, are modulated out of phase in order to force a local modulation of current-density at constant input power. Off-axis deposition (ρ dep = 0.24) is performed to avoid the central region, where the low heat flux would make transport analysis difficult. In addition some sawteeth control is achieved in this way. A significant impact on local shear is achieved with I ECCD ∼ 0.1I OH , even when the modulation period is much shorter than the current diffusion time across the whole plasma radius. The main result is that although source (heat and particle) terms are constant, both electron density and temperature are modulated during alternated ECCD. Once equilibrium effects are taken into account for appropriate mapping of Thomson scattering measurements onto flux coordinates, modulation of T e and electron pressure, peaked on-axis, is confirmed at all radii internal to EC deposition. The best confinement occurs for co-injection, in which case a local decrease (∼55%) in the magnetic shear causes a decrease in the electron thermal diffusivity of a similar amount (∼65%)

Colwellia psychrerythraea strains from distant deep sea basins show adaptation to local conditions

Directory of Open Access Journals (Sweden)

Stephen M Techtmann

2016-05-01

Full Text Available Many studies have shown that microbes, which share nearly identical 16S rRNA genes, can have highly divergent genomes. Microbes from distinct parts of the ocean also exhibit biogeographic patterning. Here we seek to better understand how certain microbes from the same species have adapted for growth under local conditions. The phenotypic and genomic heterogeneity of three strains of Colwellia psychrerythraea was investigated in order to understand adaptions to local environments. Colwellia are psychrophilic heterotrophic marine bacteria ubiquitous in cold marine ecosystems. We have recently isolated two Colwellia strains: ND2E from the Eastern Mediterranean and GAB14E from the Great Australian Bight. The 16S rRNA sequence of these two strains were greater than 98.2% identical to the well-characterized C. psychrerythraea 34H, which was isolated from arctic sediments. Salt tolerance, and carbon source utilization profiles for these strains were determined using Biolog Phenotype Microarrays’. These strains exhibited distinct salt tolerance, which was not associated with the salinity of sites of isolation. The carbon source utilization profiles were distinct with less than half of the tested carbon sources being metabolized by all three strains. Whole genome sequencing revealed that the genomes of these three strains were quite diverse with some genomes having up to 1600 strain-specific genes. Many genes involved in degrading strain-specific carbon sources were identified. There appears to be a link between carbon source utilization and location of isolation with distinctions observed between the Colwellia isolate recovered from sediment compared to water column isolates.

Local, atomic-level elastic strain measurements of metallic glass thin films by electron diffraction

Energy Technology Data Exchange (ETDEWEB)

Ebner, C. [Physics of Nanostructured Materials, Faculty of Physics, University of Vienna, Boltzmanngasse 5, 1090 Vienna (Austria); Sarkar, R. [Department of Materials Science and Engineering, School for Engineering of Matter Transport and Energy, Arizona State University, Tempe 85287 (United States); Rajagopalan, J. [Department of Materials Science and Engineering, School for Engineering of Matter Transport and Energy, Arizona State University, Tempe 85287 (United States); Department of Mechanical and Aerospace Engineering, School for Engineering of Matter Transport and Energy, Arizona State University, Tempe 85287 (United States); Rentenberger, C., E-mail: christian.rentenberger@univie.ac.at [Physics of Nanostructured Materials, Faculty of Physics, University of Vienna, Boltzmanngasse 5, 1090 Vienna (Austria)

2016-06-15

A novel technique is used to measure the atomic-level elastic strain tensor of amorphous materials by tracking geometric changes of the first diffuse ring of selected area electron diffraction patterns (SAD). An automatic procedure, which includes locating the centre and fitting an ellipse to the diffuse ring with sub-pixel precision is developed for extracting the 2-dimensional strain tensor from the SAD patterns. Using this technique, atomic-level principal strains from micrometre-sized regions of freestanding amorphous Ti{sub 0.45}Al{sub 0.55} thin films were measured during in-situ TEM tensile deformation. The thin films were deformed using MEMS based testing stages that allow simultaneous measurement of the macroscopic stress and strain. The calculated atomic-level principal strains show a linear dependence on the applied stress, and good correspondence with the measured macroscopic strains. The calculated Poisson’s ratio of 0.23 is reasonable for brittle metallic glasses. The technique yields a strain accuracy of about 1×10{sup −4} and shows the potential to obtain localized strain profiles/maps of amorphous thin film samples. - Highlights: • A TEM method to measure elastic strain in metallic glass films is proposed. • Method is based on tracking geometric changes in TEM diffraction patterns. • An automatic procedure is developed for extracting the local strain tensor. • Atomic-level strain in amorphous TiAl film was analysed during in-situ deformation. • Capability of the method to obtain micrometer scale strain profiles/maps is shown.

Shear-wave elastography for breast masses: local shear wave speed (m/sec) versus Young modulus (kPa).

Science.gov (United States)

Youk, Ji Hyun; Son, Eun Ju; Park, Ah Young; Kim, Jeong-Ah

2014-01-01

To evaluate and compare the performance of shear-wave elastography (SWE) for breast masses using the local shear wave speed (m/sec) vs. Young modulus (kPa). A total of 130 breast lesions in 123 women who underwent SWE before ultrasound- guided core needle biopsy or surgical excision were included. With the region-of-interest placed over the stiffest areas of the lesion on SWE, the quantitative mean, maximum, and standard deviation (SD) of the elasticity values were measured in kPa and m/sec for each lesion. The SD was also measured with the region-of-interest including the whole breast lesion (wSD). The area under the receiver operating characteristic curve (AUC), sensitivity, and specificity of each elasticity value measured in kPa and m/sec were compared. Of the 130 lesions, 49 (37.7%) were malignant and 81 (62.3%) were benign. The AUCs for the mean, maximum, and SD of the elasticity values using kPa and m/sec did not differ significantly: mean, 0.974 vs. 0.974; maximum, 0.960 vs. 0.976; SD, 0.916 vs. 0.916. However, the AUC for wSD showed a significant difference: 0.964 (kPa) vs. 0.960 (m/sec) (P=0.036). There was no significant difference in the sensitivity and specificity of the mean, maximum, and wSD of the elasticity values. However, the specificity of the SD was significantly different between the two different measurements: 95.1% (kPa) vs. 87.7% (m/sec) (P=0.031). The quantitative elasticity values measured in kPa and m/sec on SWE showed good diagnostic performance. The specificity of the SD and AUC of the wSD measured in kPa were significantly higher than those measured in m/sec.

Shear-wave elastography for breast masses: local shear wave speed (m/sec) versus Young modulus (kPa)

Energy Technology Data Exchange (ETDEWEB)

Youk, Ji Hyun; Son, Eun Ju; Park, Ah Young; Kim, Jeong Ah [Dept. of Radiology, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul (Korea, Republic of)

2014-03-15

To evaluate and compare the performance of shear-wave elastography (SWE) for breast masses using the local shear wave speed (m/sec) vs. Young modulus (kPa). A total of 130 breast lesions in 123 women who underwent SWE before ultrasound- guided core needle biopsy or surgical excision were included. With the region-of-interest placed over the stiffest areas of the lesion on SWE, the quantitative mean, maximum, and standard deviation (SD) of the elasticity values were measured in kPa and m/sec for each lesion. The SD was also measured with the region-of-interest including the whole breast lesion (wSD). The area under the receiver operating characteristic curve (AUC), sensitivity, and specificity of each elasticity value measured in kPa and m/sec were compared. Of the 130 lesions, 49 (37.7%) were malignant and 81 (62.3%) were benign. The AUCs for the mean, maximum, and SD of the elasticity values using kPa and m/sec did not differ significantly: mean, 0.974 vs. 0.974; maximum, 0.960 vs. 0.976; SD, 0.916 vs. 0.916. However, the AUC for wSD showed a significant difference: 0.964 (kPa) vs. 0.960 (m/sec) (P=0.036). There was no significant difference in the sensitivity and specificity of the mean, maximum, and wSD of the elasticity values. However, the specificity of the SD was significantly different between the two different measurements: 95.1% (kPa) vs. 87.7% (m/sec) (P=0.031). The quantitative elasticity values measured in kPa and m/sec on SWE showed good diagnostic performance. The specificity of the SD and AUC of the wSD measured in kPa were significantly higher than those measured in m/sec.

Shear-wave elastography for breast masses: local shear wave speed (m/sec) versus Young modulus (kPa)

International Nuclear Information System (INIS)

Youk, Ji Hyun; Son, Eun Ju; Park, Ah Young; Kim, Jeong Ah

2014-01-01

To evaluate and compare the performance of shear-wave elastography (SWE) for breast masses using the local shear wave speed (m/sec) vs. Young modulus (kPa). A total of 130 breast lesions in 123 women who underwent SWE before ultrasound- guided core needle biopsy or surgical excision were included. With the region-of-interest placed over the stiffest areas of the lesion on SWE, the quantitative mean, maximum, and standard deviation (SD) of the elasticity values were measured in kPa and m/sec for each lesion. The SD was also measured with the region-of-interest including the whole breast lesion (wSD). The area under the receiver operating characteristic curve (AUC), sensitivity, and specificity of each elasticity value measured in kPa and m/sec were compared. Of the 130 lesions, 49 (37.7%) were malignant and 81 (62.3%) were benign. The AUCs for the mean, maximum, and SD of the elasticity values using kPa and m/sec did not differ significantly: mean, 0.974 vs. 0.974; maximum, 0.960 vs. 0.976; SD, 0.916 vs. 0.916. However, the AUC for wSD showed a significant difference: 0.964 (kPa) vs. 0.960 (m/sec) (P=0.036). There was no significant difference in the sensitivity and specificity of the mean, maximum, and wSD of the elasticity values. However, the specificity of the SD was significantly different between the two different measurements: 95.1% (kPa) vs. 87.7% (m/sec) (P=0.031). The quantitative elasticity values measured in kPa and m/sec on SWE showed good diagnostic performance. The specificity of the SD and AUC of the wSD measured in kPa were significantly higher than those measured in m/sec.

Shear at Twin Domain Boundaries in YBa2Cu3O7-x

Science.gov (United States)

Caldwell, W. A.; Tamura, N.; Celestre, R. S.; MacDowell, A. A.; Padmore, H. A.; Geballe, T. H.; Koster, G.; Batterman, B. W.; Patel, J. R.

2004-05-01

The microstructure and strain state of twin domains in YBa2Cu3O7-x are discussed based upon synchrotron white-beam x-ray microdiffraction measurements. Intensity variations of the fourfold twin splitting of Laue diffraction peaks are used to determine the twin domain structure. Strain analysis shows that interfaces between neighboring twin domains are strained in shear, whereas the interior of these domains are regions of low strain. These measurements are consistent with the orientation relationships of twin boundaries within and across domains and show that basal plane shear stresses can exceed 100MPa where twin domains meet. Our results support stress field pinning of magnetic flux vortices by twin domain boundaries.

Laboratory Studies on the Effects of Shear on Fish

Energy Technology Data Exchange (ETDEWEB)

Neitzel, Duane A.; Richmond, Marshall C.; Dauble, Dennis D.; Mueller, Robert P.; Moursund, Russell A.; Abernethy, Cary S.; Guensch, Greg R.

2000-09-20

The overall objective of our studies was to specify an index describing the hydraulic force that fish experience when subjected to a shear environment. Fluid shear is a phenomenon that is important to fish. However, elevated levels of shear may result in strain rates that injure or kill fish. At hydroelectric generating facilities, concerns have been expressed that strain rates associated with passage through turbines, spillways, and fish bypass systems may adversely affect migrating fish. Development of fish friendly hydroelectric turbines requires knowledge of the physical forces (injury mechanisms) that impact entrained fish and the fish's tolerance to these forces. It requires up-front, pre-design specifications for the environmental conditions that occur within the turbine system, in other words, determining or assuming that those conditions known to injure fish will provide the descriptions of conditions that engineers must consider in the design of a turbine system. These biological specifications must be carefully and thoroughly documented throughout the design of a fish friendly turbine. To address the development of biological specifications, we designed and built a test facility where juvenile fish could be subjected to a range of shear environments and quantified their biological response.

Phenomenological interpretation of the shear behavior of reinforced Engineered Cementitious Composite beams

DEFF Research Database (Denmark)

Paegle, Ieva; Fischer, Gregor

2016-01-01

This paper describes an experimental investigation of the shear behavior of beams consisting of steel Reinforced Engineered Cementitious Composites (R/ECC). This study investigates and quantifies the effect of ECC's strain hardening and multiple cracking behavior on the shear capacity of beams...

Effect of periodic fluctuation of soil particle rotation resistance on interface shear behaviour

International Nuclear Information System (INIS)

Ebrahimian, Babak; Noorzad, Asadollah

2010-01-01

The interface behaviour between infinite extended narrow granular layer and bounding structure is numerically investigated using finite element method. The micro-polar (Cosserat) continuum approach within the framework of elasto-plasticity is employed to remove the numerical difficulties caused by strain-softening of materials in classical continuum mechanics. Mechanical properties of cohesionless granular soil are described with Lade's model enhanced with polar terms including Cosserat rotations, curvatures and couple stresses via mean grain diameter as the internal length. The main attention of paper is laid on the influence of spatial periodic fluctuation of rotation resistance of soil particles interlocked with the surface of bounding structure on evolution and location of shear band developed inside granular body. The finite element results demonstrate that the location and evolution of shear localization in granular body is strongly affected by prescribed non-uniform micro-polar kinematic boundary conditions along the interface.

Stud-bolts strength for cell-liner design under shearing deformation

International Nuclear Information System (INIS)

Watashi, Katsumi; Nakanishi, Seiji

1991-01-01

This paper presents experimental and analytical stud-bolt strength subjected to large shearing deformation at high temperature. Tensile test result of the material, SM41B, was shown in the range of room temperature to 550degC at 10 -3 and 10 -4 m/m/s in strain rate. Shearing fracture test result of the stud-bolt is shown at room temperature and 530degC. Shearing fracture criterion was discussed based on both test results and FEM analysis result. (author)

Identifikasi Brucella abortus Isolat Lokal dengan Brucella abortus Strain Specific-Polymerase Chain Reaction (IDENTIFICATION OF LOCAL ISOLATES OF BRUCELLA ABORTUS USING BRUCELLA ABORTUS STRAIN SPECIFIC-POLYMERASE CHAIN REACTION ASSAY)

OpenAIRE

Susan Maphilindawati Noor; Pratiwi Pujilestari Sudarmono; Asmarani Kusumawati; Anis Karuniawati

2014-01-01

Brucella abortus Strain Specific-Polymerase Chain Reaction (BaSS-PCR) is a single multiplex PCRtechnique which able to identify and differentiate between Brucella abortus field strains (biovar 1, 2, and4), B. abortus vaccine strains, Brucella species, and non-Brucella species. In this study, BaSS-PCR wasapplied to identify local isolates of B. abortus in order to investigate the B. abortus strains that infectedcattle in Indonesia. Fifty local strains of B.abortus isolated from infected cattle...

A TEM method for analyzing local strain fields in irradiated materials

International Nuclear Information System (INIS)

Bennetch, J.I.; Jesser, W.A.

1983-01-01

Of great interest to the field of fracture mechanics is the strain field in front of a crack tip. In irradiated materials, cavities which naturally form as a result of radiation provide convenient internal markers. If a miniaturized irradiated tensile sample is pulled in situ in a transmission electron microscope (TEM), both the relative displacement of these cavities and their distortion in shape provide information on localized strain on a microscopic level. In addition, the TEM method allows direct correlation of active slip systems with crack propagation characteristics. To illustrate this method a strain field map was constructed about a crack propagating in a helium irradiated type 316 stainless steel sample containing large cavities. (orig.)

In situ monitoring of localized shear stress and fluid flow within developing tissue constructs by Doppler optical coherence tomography

Science.gov (United States)

Jia, Yali; Bagnaninchi, Pierre O.; Wang, Ruikang K.

2008-02-01

Mechanical stimuli can be introduced to three dimensional (3D) cell cultures by use of perfusion bioreactor. Especially in musculoskeletal tissues, shear stress caused by fluid flow generally increase extra-cellular matrix (ECM) production and cell proliferation. The relationship between the shear stress and the tissue development in situ is complicated because of the non-uniform pore distribution within the cell-seeded scaffold. In this study, we firstly demonstrated that Doppler optical coherence tomography (DOCT) is capable of monitoring localized fluid flow and shear stress in the complex porous scaffold by examining their variation trends at perfusion rate of 5, 8, 10 and 12 ml/hr. Then, we developed the 3D porous cellular constructs, cell-seeded chitosan scaffolds monitored during several days by DOCT. The fiber based fourier domain DOCT employed a 1300 nm superluminescent diode with a bandwidth of 52 nm and a xyz resolution of 20×20×15 μm in free space. This setup allowed us not only to assess the cell growth and ECM deposition by observing their different scattering behaviors but also to further investigate how the cell attachment and ECM production has the effect on the flow shear stress and the relationship between flow rate and shear stress in the developing tissue construct. The possibility to monitor continuously the constructs under perfusion will easily indicate the effect of flow rate or shear stress on the cell viability and cell proliferation, and then discriminate the perfusion parameters affecting the pre-tissue formation rate growth.

Lattice Boltzmann simulation of shear-induced particle migration in plane Couette-Poiseuille flow: Local ordering of suspension

Science.gov (United States)

Chun, Byoungjin; Kwon, Ilyoung; Jung, Hyun Wook; Hyun, Jae Chun

2017-12-01

The shear-induced migration of concentrated non-Brownian monodisperse suspensions in combined plane Couette-Poiseuille (C-P) flows is studied using a lattice Boltzmann simulation. The simulations are mainly performed for a particle volume fraction of ϕbulk = 0.4 and H/a = 44.3, 23.3, where H and a denote the channel height and radius of suspended particles, respectively. The simulation method is validated in two simple flows, plane Poiseuille and plane Couette flows. In the Poiseuille flow, particles migrate to the mid-plane of the channel where the local concentration is close to the limit of random-close-packing, and a random structure is also observed at the plane. In the Couette flow, the particle distribution remains in the initial uniform distribution. In the combined C-P flows, the behaviors of migration are categorized into three groups, namely, Poiseuille-dominant, Couette-dominant, and intermediate regimes, based on the value of a characteristic force, G, where G denotes the relative magnitude of the body force (P) against the wall-driving force (C). With respect to the Poiseuille-dominant regime, the location of the maximum concentration is shifted from the mid-plane to the lower wall moving in the same direction as the external body force, when G decreases. With respect to the Couette-dominant regime, the behavior is similar to that of a simple shear flow with the exception that a slightly higher concentration of particles is observed near the lower wall. However, with respect to the intermediate value of G, several layers of highly ordered particles are unexpectedly observed near the lower wall where the plane of maximum concentration is located. The locally ordered structure is mainly due to the lateral migration of particles and wall confinement. The suspended particles migrate toward a vanishingly small shear rate at the wall, and they are consequently layered into highly ordered two-dimensional structures at the high local volume fraction.

High fluid shear strain causes injury in silver shark: Preliminary implications for Mekong hydropower turbine design

Energy Technology Data Exchange (ETDEWEB)

Baumgartner, L. J. [New South Wales Department of Primary Industries, Narrandera Fisheries Centre, Narrandera NSW Australia; Institute of Land, Water and Society, Charles Sturt University, Albury NSW Australia; Thorncraft, G. [Faculty of Agriculture, Forestry and Fisheries, National University of Laos, Vientiane Lao People’s Democratic Republic; Phonekhampheng, O. [Faculty of Agriculture, Forestry and Fisheries, National University of Laos, Vientiane Lao People’s Democratic Republic; Boys, C. [New South Wales Department of Primary Industries, Port Stephens Fisheries Institute, Nelson Bay NSW Australia; Navarro, A. [Institute of Land, Water and Society, Charles Sturt University, Albury NSW Australia; Robinson, W. [Institute of Land, Water and Society, Charles Sturt University, Albury NSW Australia; Brown, R. [Pacific Northwest National Laboratory, Richland WA USA; Deng, Z. D. [Pacific Northwest National Laboratory, Richland WA USA

2017-02-09

Fluid shear arises when two bodies of water, travelling at different velocities, intersect. Fish entrained at the interface of these two water masses will experience shear stress; which can be harmful. The stress magnitude is dependent on waterbody mass and velocity; with the fish impact largely related to body size. Elevated shear stress occurs where rapidly flowing water passes near spillways, across screens, within turbine draft tubes or other passage routes. A flume was used to determine critical tolerances of silver shark (Balantiocheilos melanopterus) to different shear stress rates generated by a high velocity jet. Fish experienced higher levels of injury and mortality as shear stress was increased. Excessive shear forces had damaging impacts on fish. Mortality occurred at shear levels higher that 600/s. It is important that developers should attempt to model potential shear profiles expected during turbine passage in selected designs. These data will be critical to determine potential impacts on fish. If the likelihood of adverse impact is high, then alternative designs which have lower shear stress could be explored.

Experimental demonstration of a semi-brittle origin for crustal strain transients

Science.gov (United States)

Reber, J. E.; Lavier, L. L.; Hayman, N. W.

2015-12-01

Tectonic motions that give rise to destructive earthquakes and enigmatic transient slip events are commonly explained by friction laws that describe slip on fault surfaces and gouge-filled zones. Friction laws with the added effects of pore fluid pressure, shear heating, and chemical reactions as currently applied do not take into account that over a wide range of pressure and temperature conditions rocks deform following a complex mixed brittle-ductile rheology. In semi-brittle materials, such as polymineralic rocks, elasto-plastic and visco-elastic defamation can be observed simultaneously in different phases of the material. Field observations of such semi-brittle rocks at the mesoscale have shown that for a given range of composition, temperature, and pressure, the formation of fluid-filled brittle fractures and veins can precede and accompany the development of localized ductile flow. We propose that the coexistence of brittle and viscous behavior controls some of the physical characteristics of strain transients and slow slip events. Here we present results from shear experiments on semi-brittle rock analogues investigating the effect of yield stress on fracture propagation and connection, and how this can lead to reoccurring strain transients. During the experiments we monitor the evolution of fractures and flow as well as the force development in the system. We show that the nature of localized slip and flow in semi-brittle materials depends on the initiation and formation of mode I and II fractures and does not involve frictional behavior, supporting an alternative mechanism for the development of tectonic strain transients.

Local strain in front of cracks in the case of creep fatigue

International Nuclear Information System (INIS)

Rie Kyongtschong; Olfe, J.

1993-01-01

In-situ measurements of strain fields in front of cracks were performed for high temperature Low Cycle Fatigue (LCF) with different hold times by means of a grid method. The tests were carried out on the austenitic stainless steel 304 L and the ferritic steel X22 CrMoV 12 1. Simultaneous observation of crack growth leads to a correlation between crack growth and local strain. The interaction of creep and fatigue related to strain concentration at the crackk tip and crack growth was discussed. A model is proposed which is based on the formation of cavities on grain boundaries. (orig.) [de

The role of local strains from prior cold work on stress corrosion cracking of α-brass in Mattsson's solution

International Nuclear Information System (INIS)

Ulaganathan, Jaganathan; Newman, Roger C.

2014-01-01

The dynamic strain rate ahead of a crack tip formed during stress corrosion cracking (SCC) under a static load is assumed to arise from the crack propagation. The strain surrounding the crack tip would be redistributed as the crack grows, thereby having the effect of dynamic strain. Recently, several studies have shown cold work to cause accelerated crack growth rates during SCC, and the slip-dissolution mechanism has been widely applied to account for this via a supposedly increased crack-tip strain rate in cold worked material. While these interpretations consider cold work as a homogeneous effect, dislocations are generated inhomogeneously within the microstructure during cold work. The presence of grain boundaries results in dislocation pile-ups that cause local strain concentrations. The local strains generated from cold working α-brass by tensile elongation were characterized using electron backscatter diffraction (EBSD). The role of these local strains in SCC was studied by measuring the strain distributions from the same regions of the sample before cold work, after cold work, and after SCC. Though, the cracks did not always initiate or propagate along boundaries with pre-existing local strains from the applied cold work, the local strains surrounding the cracked boundaries had contributions from both the crack propagation and the prior cold work. - Highlights: • Plastic strain localization has a complex relationship with SCC susceptibility. • Surface relief created by cold work creates its own granular strain localization. • Cold work promotes crack growth but several other factors are involved

Enhancing Rotational Diffusion Using Oscillatory Shear

KAUST Repository

Leahy, Brian D.

2013-05-29

Taylor dispersion - shear-induced enhancement of translational diffusion - is an important phenomenon with applications ranging from pharmacology to geology. Through experiments and simulations, we show that rotational diffusion is also enhanced for anisotropic particles in oscillatory shear. This enhancement arises from variations in the particle\\'s rotation (Jeffery orbit) and depends on the strain amplitude, rate, and particle aspect ratio in a manner that is distinct from the translational diffusion. This separate tunability of translational and rotational diffusion opens the door to new techniques for controlling positions and orientations of suspended anisotropic colloids. © 2013 American Physical Society.

Viscosity, granular-temperature, and stress calculations for shearing assemblies of inelastic, frictional disks

International Nuclear Information System (INIS)

Walton, O.R.; Braun, R.L.

1986-01-01

Employing nonequilibrium molecular-dynamics methods the effects of two energy loss mechanisms on viscosity, stress, and granular-temperature in assemblies of nearly rigid, inelastic frictional disks undergoing steady-state shearing are calculated. Energy introduced into the system through forced shearing is dissipated by inelastic normal forces or through frictional sliding during collisions resulting in a natural steady-state kinetic energy density (granular-temperature) that depends on the density and shear rate of the assembly and on the friction and inelasticity properties of the disks. The calculations show that both the mean deviatoric particle velocity and the effective viscosity of a system of particles with fixed friction and restitution coefficients increase almost linearly with strain rate. Particles with a velocity-dependent coefficient of restitution show a less rapid increase in both deviatoric velocity and viscosity as strain rate increases. Particles with highly dissipative interactions result in anisotropic pressure and velocity distributions in the assembly, particularly at low densities. At very high densities the pressure also becomes anisotropic due to high contact forces perpendicular to the shearing direction. The mean rotational velocity of the frictional disks is nearly equal to one-half the shear rate. The calculated ratio of shear stress to normal stress varies significantly with density while the ratio of shear stress to total pressure shows much less variation. The inclusion of surface friction (and thus particle rotation) decreases shear stress at low density but increases shear stress under steady shearing at higher densities

Impedance method for measuring shear elasticity of liquids

Science.gov (United States)

Badmaev, B. B.; Dembelova, T. S.; Damdinov, B. B.; Gulgenov, Ch. Zh.

2017-11-01

Experimental results of studying low-frequency (74 kHz) shear elasticity of polymer liquids by the impedance method (analogous to the Mason method) are presented. A free-volume thick liquid layer is placed on the horizontal surface of a piezoelectric quartz crystal with dimensions 34.7 × 12 × 5.5 cm. The latter performs tangential vibrations at resonance frequency. The liquid layer experiences shear strain, and shear waves should propagate in it. From the theory of the method, it follows that, with an increase in the layer thickness, both real and imaginary resonance frequency shifts should exhibit damped oscillations and tend to limiting values. For the liquids under study, the imaginary frequency shift far exceeds the real one, which testifies to the presence of bulk shear elasticity.

Living bacteria rheology: Population growth, aggregation patterns, and collective behavior under different shear flows

Science.gov (United States)

Patrício, P.; Almeida, P. L.; Portela, R.; Sobral, R. G.; Grilo, I. R.; Cidade, T.; Leal, C. R.

2014-08-01

The activity of growing living bacteria was investigated using real-time and in situ rheology—in stationary and oscillatory shear. Two different strains of the human pathogen Staphylococcus aureus—strain COL and its isogenic cell wall autolysis mutant, RUSAL9—were considered in this work. For low bacteria density, strain COL forms small clusters, while the mutant, presenting deficient cell separation, forms irregular larger aggregates. In the early stages of growth, when subjected to a stationary shear, the viscosity of the cultures of both strains increases with the population of cells. As the bacteria reach the exponential phase of growth, the viscosity of the cultures of the two strains follows different and rich behaviors, with no counterpart in the optical density or in the population's colony-forming units measurements. While the viscosity of strain COL culture keeps increasing during the exponential phase and returns close to its initial value for the late phase of growth, where the population stabilizes, the viscosity of the mutant strain culture decreases steeply, still in the exponential phase, remains constant for some time, and increases again, reaching a constant plateau at a maximum value for the late phase of growth. These complex viscoelastic behaviors, which were observed to be shear-stress-dependent, are a consequence of two coupled effects: the cell density continuous increase and its changing interacting properties. The viscous and elastic moduli of strain COL culture, obtained with oscillatory shear, exhibit power-law behaviors whose exponents are dependent on the bacteria growth stage. The viscous and elastic moduli of the mutant culture have complex behaviors, emerging from the different relaxation times that are associated with the large molecules of the medium and the self-organized structures of bacteria. Nevertheless, these behaviors reflect the bacteria growth stage.

Manufacturing and Shear Response Characterization of Carbon Nanofiber Modified CFRP Using the Out-of-Autoclave-Vacuum-Bag-Only Cure Process

Science.gov (United States)

McDonald, Erin E.; Wallace, Landon F.; Hickman, Gregory J. S.; Hsiao, Kuang-Ting

2014-01-01

The interlaminar shear response is studied for carbon nanofiber (CNF) modified out-of-autoclave-vacuum-bag-only (OOA-VBO) carbon fiber reinforced plastic (CFRP). Commercial OOA-VBO prepregs were coated with a CNF modified epoxy solution and a control epoxy solution without CNF to make CNF modified samples and control samples, respectively. Tensile testingwas used to study the in-plane shear performance of [±45°]4s composite laminates. Significant difference in failure modes between the control and CNF modified CFRPs was identified. The control samples experienced half-plane interlaminar delamination, whereas the CNF modified samples experienced a localized failure in the intralaminar region. Digital image correlation (DIC) surface strain results of the control sample showed no further surface strain increase along the delaminated section when the sample was further elongated prior to sample failure. On the other hand, the DIC results of the CNF modified sample showed that the surface strain increased relatively and uniformly across the CFRP as the sample was further elongated until sample failure. The failure mode evidence along with microscope pictures indicated that the CNF modification acted as a beneficial reinforcement inhibiting interlaminar delamination. PMID:24688435

Manufacturing and Shear Response Characterization of Carbon Nanofiber Modified CFRP Using the Out-of-Autoclave-Vacuum-Bag-Only Cure Process

Directory of Open Access Journals (Sweden)

Erin E. McDonald

2014-01-01

Full Text Available The interlaminar shear response is studied for carbon nanofiber (CNF modified out-of-autoclave-vacuum-bag-only (OOA-VBO carbon fiber reinforced plastic (CFRP. Commercial OOA-VBO prepregs were coated with a CNF modified epoxy solution and a control epoxy solution without CNF to make CNF modified samples and control samples, respectively. Tensile testingwas used to study the in-plane shear performance of [±45°]4s composite laminates. Significant difference in failure modes between the control and CNF modified CFRPs was identified. The control samples experienced half-plane interlaminar delamination, whereas the CNF modified samples experienced a localized failure in the intralaminar region. Digital image correlation (DIC surface strain results of the control sample showed no further surface strain increase along the delaminated section when the sample was further elongated prior to sample failure. On the other hand, the DIC results of the CNF modified sample showed that the surface strain increased relatively and uniformly across the CFRP as the sample was further elongated until sample failure. The failure mode evidence along with microscope pictures indicated that the CNF modification acted as a beneficial reinforcement inhibiting interlaminar delamination.

Manufacturing and shear response characterization of carbon nanofiber modified CFRP using the out-of-autoclave-vacuum-bag-only cure process.

Science.gov (United States)

McDonald, Erin E; Wallace, Landon F; Hickman, Gregory J S; Hsiao, Kuang-Ting

2014-01-01

The interlaminar shear response is studied for carbon nanofiber (CNF) modified out-of-autoclave-vacuum-bag-only (OOA-VBO) carbon fiber reinforced plastic (CFRP). Commercial OOA-VBO prepregs were coated with a CNF modified epoxy solution and a control epoxy solution without CNF to make CNF modified samples and control samples, respectively. Tensile testing was used to study the in-plane shear performance of [± 45°]4s composite laminates. Significant difference in failure modes between the control and CNF modified CFRPs was identified. The control samples experienced half-plane interlaminar delamination, whereas the CNF modified samples experienced a localized failure in the intralaminar region. Digital image correlation (DIC) surface strain results of the control sample showed no further surface strain increase along the delaminated section when the sample was further elongated prior to sample failure. On the other hand, the DIC results of the CNF modified sample showed that the surface strain increased relatively and uniformly across the CFRP as the sample was further elongated until sample failure. The failure mode evidence along with microscope pictures indicated that the CNF modification acted as a beneficial reinforcement inhibiting interlaminar delamination.

Room Temperature Shear Band Development in Highly Twinned Wrought Magnesium AZ31B Sheet

Science.gov (United States)

Scott, Jon; Miles, Michael; Fullwood, David; Adams, Brent; Khosravani, Ali; Mishra, Raja K.

2013-01-01

Failure mechanisms were studied in wrought AZ31B magnesium alloy after forming under different strain paths. Optical micrographs were used to observe the shear band formation and regions of high twin density in samples strained under uniaxial, biaxial, and plane strain conditions. Interrupted testing at 4 pct effective strain increments, until failure, was used to observe the evolution of the microstructure. The results showed that shear bands, with a high percentage of twinned grains, appeared early in the samples strained under biaxial or plane strain tension. These bands are similar to those seen in uniaxial tension specimens just prior to failure where the uniaxial tensile ductility was much greater than that observed for plane strain or biaxial tension conditions. A forming limit diagram for AZ31B, which was developed from the strain data, showed that plane strain and biaxial tension had very similar limit strains; this contrasts with materials like steel or aluminum alloys, which typically have greater ductility in biaxial tension compared to plane strain tension.

Piezoelectric dynamic strain monitoring for detecting local seismic damage in steel buildings

International Nuclear Information System (INIS)

Kurata, Masahiro; Li, Xiaohua; Fujita, Kohei; Yamaguchi, Mayako

2013-01-01

This research presents a methodology for damage detection along with a sensing system for monitoring seismic damage in steel buildings. The system extracts the location and extent of local damage, such as fracture at a beam–column connection, from changes in the bending moment distribution in a steel moment-resisting frame. We developed a dynamic strain-based sensing system utilizing piezoelectric film sensors and wireless sensing techniques to estimate the bending moments resisted by individual structural members under small amplitude loadings such as ambient vibrations and minor earthquakes. We introduce a new damage index that extracts local damage information from the comparative study of the dynamic strain responses of the structural members before and after a large earthquake event. The damage detection scheme was examined both analytically and numerically using a simple frame example. Then, the entire local damage detection scheme was verified through a series of vibration tests using a one-quarter-scale steel testbed that simulated seismic damage at member ends. (paper)

Characterization of Local Strain around Through-Silicon Via Interconnects by Using X-ray Microdiffraction

Science.gov (United States)

Nakatsuka, Osamu; Kitada, Hideki; Kim, Youngsuk; Mizushima, Yoriko; Nakamura, Tomoji; Ohba, Takayuki; Zaima, Shigeaki

2011-05-01

We have demonstrated the characterization of the local strain structure in thinned Si layers for wafer-on-a-wafer (WOW) applications by using X-ray microdiffraction with a synchrotron radiation source. The microdiffraction reveals the fluctuation of strains in the thin Si layer around through-silicon via (TSV) interconnects with a sub-micrometer scale. We can separately estimated the in-plane and out-of-plane strain structures in the Si layer, and found that the anisotropic strain is induced in the Si layer between the TSV interconnects.

Application and Analysis of Measurement Model for Calibrating Spatial Shear Surface in Triaxial Test

Science.gov (United States)

Zhang, Zhihua; Qiu, Hongsheng; Zhang, Xiedong; Zhang, Hang

2017-12-01

Discrete element method has great advantages in simulating the contacts, fractures, large displacement and deformation between particles. In order to analyze the spatial distribution of the shear surface in the three-dimensional triaxial test, a measurement model is inserted in the numerical triaxial model which is generated by weighted average assembling method. Due to the non-visibility of internal shear surface in laboratory, it is largely insufficient to judge the trend of internal shear surface only based on the superficial cracks of sheared sample, therefore, the measurement model is introduced. The trend of the internal shear zone is analyzed according to the variations of porosity, coordination number and volumetric strain in each layer. It shows that as a case study on confining stress of 0.8 MPa, the spatial shear surface is calibrated with the results of the rotated particle distribution and the theoretical value with the specific characteristics of the increase of porosity, the decrease of coordination number, and the increase of volumetric strain, which represents the measurement model used in three-dimensional model is applicable.

Origins of Shear Jamming for Frictional Grains

Science.gov (United States)

Wang, Dong; Zheng, Hu; Ren, Jie; Dijksman, Joshua; Bares, Jonathan; Behringer, Robert

2016-11-01

Granular systems have been shown to be able to behave like solids, under shear, even when their densities are below the critical packing fraction for frictionless isotropic jamming. To understand such a phenomena, called shear jamming, the question we address here is: how does shear bring a system from a unjammed state to a jammed state, where the coordination number, Z, is no less than 3, the isotropic jamming point for frictional grains? Since Z can be used to distinguish jammed states from unjammed ones, it is vital to understand how shear increases Z. We here propose a set of three particles in contact, denoted as a trimer, as the basic unit to characterize the deformation of the system. Trimers, stabilized by inter-grain friction, fail under a certain amount of shear and bend to make extra contacts to regain stability. By defining a projection operator of the opening angle of the trimer to the compression direction in the shear, O, we see a systematically linear decrease of this quantity with respect to shear strain, demonstrating the bending of trimers as expected. In addition, the average change of O from one shear step to the next shows a good collapse when plotted against Z, indicating a universal behavior in the process of shear jamming. We acknowledge support from NSF DMR1206351, NASA NNX15AD38G, the William M. Keck Foundation and a RT-MRSEC Fellowship.

Screening local Lactobacilli from Iran in terms of production of lactic acid and identification of superior strains

Directory of Open Access Journals (Sweden)

Fatemeh Soleimanifard

2015-12-01

Full Text Available Introduction: Lactobacilli are a group of lactic acid bacteria that their final product of fermentation is lactic acid. The objective of this research is selection of local Lactobacilli producing L (+ lactic acid. Materials and methods: In this research the local strains were screened based on the ability to produce lactic acid. The screening was performed in two stages. The first stage was the titration method and the second stage was the enzymatic method. The superior strains obtained from titration method were selected to do enzymatic test. Finally, the superior strains in the second stage (enzymatic which had the ability to produce L(+ lactic acid were identified by biochemical tests. Then, molecular identification of strains was performed by using 16S rRNA sequencing. Results: In this study, the ability of 79 strains of local Lactobacilli in terms of production of lactic acid was studied. The highest and lowest rates of lactic acid production was 34.8 and 12.4 mg/g. Superior Lactobacilli in terms of production of lactic acid ability of producing had an optical isomer L(+, the highest levels of L(+ lactic acid were with 3.99 and the lowest amount equal to 1.03 mg/g. The biochemical and molecular identification of superior strains showed that strains are Lactobacillus paracasei. Then the sequences of 16S rRNA of superior strains were reported in NCBI with accession numbers KF735654، KF735655، KJ508201and KJ508202. Discussion and conclusion: The amounts of lactic acid production by local Lactobacilli were very different and producing some of these strains on available reports showed more products. The results of this research suggest the use of superior strains of Lactobacilli for production of pure L(+ lactic acid.

Singular solutions for the rigid plastic double slip and rotation model under plane strain

Science.gov (United States)

Alexandrov, S.; Lyamina, E.

2018-02-01

In the mechanics of granular and other materials the system of equations comprising the rigid plastic double slip and rotation model together with the stress equilibrium equations under plane strain conditions forms a hyperbolic system. Boundary value problems for this system of equations can involve a frictional interface. An envelope of characteristics may coincide with this interface. In this case, the solution is singular. In particular, some components of the strain rate tensor approach infinity in the vicinity of the frictional interface. Such behavior of solutions is in qualitative agreement with experimental data that show that a narrow layer of localized plastic deformation is often generated near frictional interfaces. The present paper deals with asymptotic analysis of the aforementioned system of equations in the vicinity of an envelope of characteristics. It is shown that the shear strain rate and the spin component in a local coordinate system connected to the envelope follow an inverse square root rule in its vicinity.

Steady shear characteristic and behavior of magneto-thermo-elasticity of isotropic MR elastomers

International Nuclear Information System (INIS)

Gao, Wei; Wang, Xingzhe

2016-01-01

The magneto-thermo-elastic steady shear behaviors of isotropic smart composites of silicon rubber matrix randomly filled with ferromagnetic particles, commonly referred to as magnetorheological (MR) elastomers, are investigated experimentally and theoretically in the present study. The strip specimens of the MR elastomer composite with different ferromagnetic particle concentrations are fabricated and implemented for lap-shear tests under both magnetic and thermal fields. It is illustrated that the magneto-thermo-elastic shear modulus of the MR elastomer is markedly enhanced with the volume fraction of ferromagnetic particles and the applied external magnetic field, while the shear modulus is decreased with the environment temperature. To qualitatively elucidate the magneto-thermo-elastic shear performance of this kind of magnetic smart composites, a modified constitutive of hyperelasticity is suggested taking into account the influence of magnetic field and temperature on the magnetic potential energy and strain energy. The theoretical modeling predictions on the stress–strain behaviors for different applied magnetic fields and environment temperatures are compared to experimental observations to demonstrate a good agreement. (paper)

Stability of surface plastic flow in large strain deformation of metals

Science.gov (United States)

Viswanathan, Koushik; Udapa, Anirduh; Sagapuram, Dinakar; Mann, James; Chandrasekar, Srinivasan

We examine large-strain unconstrained simple shear deformation in metals using a model two-dimensional cutting system and high-speed in situ imaging. The nature of the deformation mode is shown to be a function of the initial microstructure state of the metal and the deformation geometry. For annealed metals, which exhibit large ductility and strain hardening capacity, the commonly assumed laminar flow mode is inherently unstable. Instead, the imposed shear is accommodated by a highly rotational flow-sinuous flow-with vortex-like components and large-amplitude folding on the mesoscale. Sinuous flow is triggered by a plastic instability on the material surface ahead of the primary region of shear. On the other hand, when the material is extensively strain-hardened prior to shear, laminar flow again becomes unstable giving way to shear banding. The existence of these flow modes is established by stability analysis of laminar flow. The role of the initial microstructure state in determining the change in stability from laminar to sinuous / shear-banded flows in metals is elucidated. The implications for cutting, forming and wear processes for metals, and to surface plasticity phenomena such as mechanochemical Rehbinder effects are discussed.

Shear wave elastography with a new reliability indicator

Directory of Open Access Journals (Sweden)

Christoph F. Dietrich

2016-09-01

Full Text Available Non-invasive methods for liver stiffness assessment have been introduced over recent years. Of these, two main methods for estimating liver fibrosis using ultrasound elastography have become established in clinical practice: shear wave elastography and quasi-static or strain elastography. Shear waves are waves with a motion perpendicular (lateral to the direction of the generating force. Shear waves travel relatively slowly (between 1 and 10 m/s. The stiffness of the liver tissue can be assessed based on shear wave velocity (the stiffness increases with the speed. The European Federation of Societies for Ultrasound in Medicine and Biology has published Guidelines and Recommendations that describe these technologies and provide recommendations for their clinical use. Most of the data available to date has been published using the Fibroscan (Echosens, France, point shear wave speed measurement using an acoustic radiation force impulse (Siemens, Germany and 2D shear wave elastography using the Aixplorer (SuperSonic Imagine, France. More recently, also other manufacturers have introduced shear wave elastography technology into the market. A comparison of data obtained using different techniques for shear wave propagation and velocity measurement is of key interest for future studies, recommendations and guidelines. Here, we present a recently introduced shear wave elastography technology from Hitachi and discuss its reproducibility and comparability to the already established technologies.

Shear wave elastography with a new reliability indicator.

Science.gov (United States)

Dietrich, Christoph F; Dong, Yi

2016-09-01

Non-invasive methods for liver stiffness assessment have been introduced over recent years. Of these, two main methods for estimating liver fibrosis using ultrasound elastography have become established in clinical practice: shear wave elastography and quasi-static or strain elastography. Shear waves are waves with a motion perpendicular (lateral) to the direction of the generating force. Shear waves travel relatively slowly (between 1 and 10 m/s). The stiffness of the liver tissue can be assessed based on shear wave velocity (the stiffness increases with the speed). The European Federation of Societies for Ultrasound in Medicine and Biology has published Guidelines and Recommendations that describe these technologies and provide recommendations for their clinical use. Most of the data available to date has been published using the Fibroscan (Echosens, France), point shear wave speed measurement using an acoustic radiation force impulse (Siemens, Germany) and 2D shear wave elastography using the Aixplorer (SuperSonic Imagine, France). More recently, also other manufacturers have introduced shear wave elastography technology into the market. A comparison of data obtained using different techniques for shear wave propagation and velocity measurement is of key interest for future studies, recommendations and guidelines. Here, we present a recently introduced shear wave elastography technology from Hitachi and discuss its reproducibility and comparability to the already established technologies.

Simulations of Granular Particles Under Cyclic Shear

Science.gov (United States)

Royer, John; Chaikin, Paul

2012-02-01

We perform molecular dynamics (MD) simulations of spherical grains subjected to cyclic, quasi-static shear in a 3D parallelepiped shear cell. This virtual shear cell is constructed out of rough, bumpy walls in order to minimize wall-induced ordering and has an open top surface to allow the packing to readily dilate or compact. Using a standard routine for MD simulations of frictional grains, we simulate over 1000 shear cycles, measuring grain displacements, the local packing density and changes in the contact network. Varying the shear amplitude and the friction coefficient between grains, we map out a phase diagram for the different types of behavior exhibited by these sheared grains. With low friction and high enough shear, the grains can spontaneously order into densely packed crystals. With low shear and increasing friction the packing remains disordered, yet the grains arrange themselves into configurations which exhibit limit cycles where all grains return to the same position after each full shear cycle. At higher shear and friction there is a transition to a diffusive state, where grains continue rearrange and move throughout the shear cell.

One-dimensional motion of a material with a strain theshold

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A. Farina

2007-12-01

Full Text Available We consider the one-dimensional shearing motion of a material exhibiting elastic behaviour when the stress is below some threshold. The threshold represents a limit to the deformability, i.e. no further deformation can occur on increasing the stress. The mathematical formulation leads to a free boundary problem for the wave equation, whose structure depends on whether the stress (and the velocity are continuous across the propagating interface for the strain threshold .Local existence and uniqueness are proved for the continuous case (in which the interface propagation is subsonic. Some explicit solutions are calculated for another case (with a supersonic interface. It is shown that the model with strain threshold is never the limit of hyperelastic systems.

Exact solutions for oscillatory shear sweep behaviors of complex fluids from the Oldroyd 8-constant framework

Science.gov (United States)

Saengow, Chaimongkol; Giacomin, A. Jeffrey

2018-03-01

In this paper, we provide a new exact framework for analyzing the most commonly measured behaviors in large-amplitude oscillatory shear flow (LAOS), a popular flow for studying the nonlinear physics of complex fluids. Specifically, the strain rate sweep (also called the strain sweep) is used routinely to identify the onset of nonlinearity. By the strain rate sweep, we mean a sequence of LAOS experiments conducted at the same frequency, performed one after another, with increasing shear rate amplitude. In this paper, we give exact expressions for the nonlinear complex viscosity and the corresponding nonlinear complex normal stress coefficients, for the Oldroyd 8-constant framework for oscillatory shear sweeps. We choose the Oldroyd 8-constant framework for its rich diversity of popular special cases (we list 18 of these). We evaluate the Fourier integrals of our previous exact solution to get exact expressions for the real and imaginary parts of the complex viscosity, and for the complex normal stress coefficients, as functions of both test frequency and shear rate amplitude. We explore the role of infinite shear rate viscosity on strain rate sweep responses for the special case of the corotational Jeffreys fluid. We find that raising η∞ raises the real part of the complex viscosity and lowers the imaginary. In our worked examples, we thus first use the corotational Jeffreys fluid, and then, for greater accuracy, we use the Johnson-Segalman fluid, to describe the strain rate sweep response of molten atactic polystyrene. For our comparisons with data, we use the Spriggs relations to generalize the Oldroyd 8-constant framework to multimode. Our generalization yields unequivocally, a longest fluid relaxation time, used to assign Weissenberg and Deborah numbers to each oscillatory shear flow experiment. We then locate each experiment in the Pipkin space.

Yielding and flow of sheared colloidal glasses

International Nuclear Information System (INIS)

Petekidis, G; Vlassopoulos, D; Pusey, P N

2004-01-01

We have studied some of the rheological properties of suspensions of hard-sphere colloids with particular reference to behaviour near the concentration of the glass transition. First we monitored the strain on the samples during and after a transient step stress. We find that, at all values of applied step stress, colloidal glasses show a rapid, apparently elastic, recovery of strain after the stress is removed. This recovery is found even in samples which have flowed significantly during stressing. We attribute this behaviour to 'cage elasticity', the recovery of the stress-induced distorted environment of any particle to a more isotropic state when the stress is removed. Second, we monitored the stress as the strain rate dot γ of flowing samples was slowly decreased. Suspensions which are glassy at rest show a stress which becomes independent of dot γ as dot γ →0. This limiting stress can be interpreted as the yield stress of the glass and agrees well both with the yield stress deduced from the step stress and recovery measurements and that predicted by a recent mode coupling theory of sheared suspensions. Thus, the behaviours under steady shearing and transient step stress both support the idea that colloidal glasses have a finite yield stress. We note however that the samples do exhibit a slow accumulation of strain due to creep at stresses below the yield stress

On localization and void coalescence as a precursor to ductile fracture.

Science.gov (United States)

Tekoğlu, C; Hutchinson, J W; Pardoen, T

2015-03-28

Two modes of plastic flow localization commonly occur in the ductile fracture of structural metals undergoing damage and failure by the mechanism involving void nucleation, growth and coalescence. The first mode consists of a macroscopic localization, usually linked to the softening effect of void nucleation and growth, in either a normal band or a shear band where the thickness of the band is comparable to void spacing. The second mode is coalescence with plastic strain localizing to the ligaments between voids by an internal necking process. The ductility of a material is tied to the strain at macroscopic localization, as this marks the limit of uniform straining at the macroscopic scale. The question addressed is whether macroscopic localization occurs prior to void coalescence or whether the two occur simultaneously. The relation between these two modes of localization is studied quantitatively in this paper using a three-dimensional elastic-plastic computational model representing a doubly periodic array of voids within a band confined between two semi-infinite outer blocks of the same material but without voids. At sufficiently high stress triaxiality, a clear separation exists between the two modes of localization. At lower stress triaxialities, the model predicts that the onset of macroscopic localization and coalescence occur simultaneously. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

Solution-mass transfer and grain boundary sliding in mafic shear zones - comparison between experiments and nature

Science.gov (United States)

Marti, Sina; Heilbronner, Renée; Stünitz, Holger; Plümper, Oliver; Drury, Martyn

2017-04-01

Grain size sensitive creep (GSSC) mechanisms are widely recognized to be the most efficient deformation mechanisms in shear zones. With or without initial fracturing and fluid infiltration, the onset of heterogeneous nucleation leading to strong grain size reduction is a frequently described process for the initiation of GSSC. Phase mixing due to reaction and heterogeneous nucleation during GSSC impedes grain growth, sustaining small grain sizes as a prerequisite for GSSC. Here we present rock deformation experiments on 'wet' plagioclase - pyroxene mixtures at T=800°C, P=1.0 and 1.5GPa and strain rates of 2e-5 - 2e-6 1/s, performed with a Griggs-type solid medium deformation apparatus. Microstructural criteria are used to show that both, grain boundary sliding (GBS) and solution-mass transfer processes are active and are interpreted to be the dominant strain accommodating processes. Displacement is localized within shear bands formed by fine-grained ( 300 - 500nm) plagioclase (Pl) and the syn-kinematic reaction products amphibole (Amph), quartz (Qz) and zoisite (Zo). We compare our experiments with a natural case - a sheared mafic pegmatite (P-T during deformation 0.7 - 0.9 GPa, 610 - 710 °C; Getsinger et al., 2013) from Northern Norway. Except for the difference in grain size of the experimental and natural samples, microstructures are strikingly alike. The experimental and natural P- and especially T-conditions are very similar. Consequently, extrapolation from experiments to nature must be made without a significant 'temperature-time' trade-off, which is normally taken advantage of when relating experimental to natural strain rates. We will discuss under which assumptions extrapolation to nature in our case is likely feasible. Syn-kinematic reactions during GBS and solution-mass transport are commonly interpreted to result in an ordered (anticlustered) phase mixture. However, phase mixing in our case is restricted: Mixing is extensive between Pl + Zo + Qz and

On the use of volumetric strain meters to infer additional characteristics of short-period seismic radiation

Science.gov (United States)

Borcherdt, R.D.; Johnston, M.J.S.; Glassmoyer, G.

1989-01-01

Volumetric strain meters (Sacks-Evertson design) are installed at 15 sites along the San Andreas fault system, to monitor long-term strain changes for earthquake prediction. Deployment of portable broadband, high-resolution digital recorders (GEOS) at several of the sites extends the detection band for volumetric strain to periods shorter than 5 ?? 10-2 sec and permits the simultaneous observation of seismic radiation fields using conventional short-period pendulum seismometers. Recordings of local and regional earthquakes indicate that dilatometers respond to P energy but not direct shear energy and that straingrams can be used to resolve superimposed reflect P and S waves for inference of wave characteristics not permitted by either sensor alone. Simultaneous measurements of incident P- and S-wave amplitudes are used to introduce a technique for single-station estimates of wave field inhomogeneity, free-surface reflection coefficients and local material P velocity. -from Authors

Tailoring the gradient ultrafine-grained structure in low-carbon steel during drawing with shear

Directory of Open Access Journals (Sweden)

G. I. Raab

2016-04-01

Full Text Available Conventional drawing and drawing with shear were conducted on the rods of low-carbon steel. Deformation by simple drawing forms basically a homogenous structure and leads to a uniform change in microhardness along the billet volume. A comparative analysis of the models of these processes showed that shear drawing of steel at room temperature reduces energy characteristics in half, normal forces on the die – by 1,8, and enhances the strain intensity from 0,5 to 1,6. During drawing with shear, strain-induced cementite dissolution occurs and a gradient structure is formed, which increases the microhardness of the surface layer up to values close to 7 000 MPa.

Mean wall-shear stress measurements using the micro-pillar shear-stress sensor MPS3

International Nuclear Information System (INIS)

Große, S; Schröder, W

2008-01-01

A new sensor to measure the mean turbulent wall-shear stress in turbulent flows is described. The wall-shear stress sensor MPS 3 has been tested in a well-defined fully developed turbulent pipe flow at Reynolds numbers Re b based on the bulk velocity U b and the pipe diameter D in the range of Re b = 10 000–20 000. The results demonstrate a convincing agreement of the mean wall-shear stress obtained with the new sensor technique with analytical and experimental results from the literature. The sensor device consists of a flexible micro-pillar that extends from the wall into the viscous sublayer. Bending due to the exerting fluid forces, the pillar-tip deflection serves as a measure for the local wall-shear stress. The sensor concept, calibration techniques, the achievable accuracy and error estimates, the fields of application and the sensor limits will be discussed. Furthermore, a first estimate of the pillar dynamic response will be derived showing the potential of the sensor to also measure the turbulent fluctuating wall-shear stress

Dynamic behavior and functional integrity tests on RC shear walls

International Nuclear Information System (INIS)

Akino, Kinji; Nasuda, Toshiaki; Shibata, Akenori.

1991-01-01

A project consisting of seven subprojects has been conducted to study the dynamic behavior and functional integrity of reinforced concrete (RC) shear walls in reactor buildings. The objective of this project is to obtain the data to improve and prepare the seismic analysis code regarding the nonlinear structural behavior and integrity of reactor buildings during and after earthquakes. The project started in April, 1986, and will end in March, 1994. Seven subprojects are strain rate test, damping characteristic test, ultimate state response test and the verification test for the test of restoring force characteristics regarding dynamic restoring force characteristics and damping performance; the restoring force characteristic test on the shear walls with openings; and pull-out strength test and the test on air leakage through concrete cracks regarding the functional integrity. The objectives of respective subprojects, the test models and the interim results are reported. Three subprojects have been completed by March, 1990. The results of these projects will be used for the overall evaluation. The strain rate test showed that the ultimate strength of shear walls increased with strain rate. A formula for estimating air flow through the cracks in walls was given by the leakage test. (K.I.)

A study of fatigue life prediction for automotive spot weldment using local strain approach

International Nuclear Information System (INIS)

Lee, Song In; Yu, Hyo Sun; Na, Sung Hun; Na, Eui Gyun

2000-01-01

The fatigue crack initiation life is studied on automotive spot weldment made from cold rolled carbon steel(SPC) sheet by using DCPDM and local strain approach. It can be found that the fatigue crack initiation behavior in spot weldment can be definitely detected by DCPDM system. The local stresses and strains are estimated by elastic-plastic FEM analysis and the alternative approximate method based on Neuber's rule were applied to predict the fatigue life of spot weldment. A satisfactory correlation between the predicted life and experimental life can be found in spot weldment within a factor of 4

Experimental study of shear bands formation in a granular material

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Nguyen Thai Binh

2017-01-01

Full Text Available We present an experimental investigation of the formation of shear bands in a granular sample submitted to a biaxial test. Our principal result is the direct observation of the bifurcation at the origin of the localization process in the material. At the bifurcation, the shear band is spatially extended: we observe a breaking of symmetry without any sudden localization of the deformation in a narrow band. Our work thus allows to clearly distinguish different phenomena: bifurcation which is a ponctual event which occurs before the peak, localization which is a process that covers a range of deformation of several percents during which the peak occurs and finally stationary shear bands which are well-defined permanent structures that can be observed at the end of the localization process, after the peak.

Elasto-plastic bond mechanics of embedded fiber optic sensors in concrete under uniaxial tension with strain localization

Science.gov (United States)

Li, Qingbin; Li, Guang; Wang, Guanglun

2003-12-01

Brittleness of the glass core inside fiber optic sensors limits their practical usage, and therefore they are coated with low-modulus softer protective materials. Protective coatings absorb a portion of the strain, and hence part of the structural strain is sensed. The study reported here corrects for this error through development of a theoretical model to account for the loss of strain in the protective coating of optical fibers. The model considers the coating as an elasto-plastic material and formulates strain transfer coefficients for elastic, elasto-plastic and strain localization phases of coating deformations in strain localization in concrete. The theoretical findings were verified through laboratory experimentation. The experimental program involved fabrication of interferometric optical fiber sensors, embedding within mortar samples and tensile tests in a closed-loop servo-hydraulic testing machine. The elasto-plastic strain transfer coefficients were employed for correction of optical fiber sensor data and results were compared with those of conventional extensometers.

Development of shear bands in amorphous-crystalline metallic alloys

International Nuclear Information System (INIS)

Pozdnyakov, V.A.

2004-01-01

A theoretical study is made into conditions of shear band evolution in amorphous-crystalline alloys with various morphological types of structural constituents. The condition of shear band evolution in thin amorphous alloys in the interior of the crystalline matrix is obtained. It is shown that a scale effect exists which manifests itself in suppression of the process of localized plastic flow with amorphous alloy thickness decreasing down to the limit. The analysis of the condition for shear band evolution in an amorphous alloy with nanocrystalline inclusions is accomplished. The relationship of a critical stress of shear band evolution to a volume fraction of disperse crystal inclusions is obtained. A consideration is also given to the evolution of shear bands in the material containing amorphous and crystalline areas of micro meter size. For the alloy with the structure of this type conditions for propagation of localized flows by a relay race type mechanism are determined [ru

Existence of localizing solutions in plasticity via the geometric singular perturbation theory

KAUST Repository

Lee, Min-Gi

2017-01-31

Shear bands are narrow zones of intense shear observed during plastic deformations of metals at high strain rates. Because they often precede rupture, their study attracted attention as a mechanism of material failure. Here, we aim to reveal the onset of localization into shear bands using a simple model from viscoplasticity. We exploit the properties of scale invariance of the model to construct a family of self-similar focusing solutions that capture the nonlinear mechanism of shear band formation. The key step is to desingularize a reduced system of singular ordinary differential equations and reduce the problem into the construction of a heteroclinic orbit for an autonomous system of three first-order equations. The associated dynamical system has fast and slow time scales, forming a singularly perturbed problem. Geometric singular perturbation theory is applied to this problem to achieve an invariant surface. The flow on the invariant surface is analyzed via the Poincaré--Bendixson theorem to construct a heteroclinic orbit.

A convergent-beam electron diffraction study of strain homogeneity in severely strained aluminum processed by equal-channel angular pressing

Energy Technology Data Exchange (ETDEWEB)

Alhajeri, Saleh N. [Materials Research Group, Faculty of Engineering and the Environment, University of Southampton, Southampton SO17 1BJ (United Kingdom); Department of Manufacturing Engineering, College of Technological Studies, PAAET, PO Box 42325, Shuwaikh 70654 (Kuwait); Fox, Alan G. [Materials Research Group, Faculty of Engineering and the Environment, University of Southampton, Southampton SO17 1BJ (United Kingdom); Mechanical Engineering Department, Asian University, 89 Moo 12, Highway 331, Banglamung, Chon Buri 20260 (Thailand); Langdon, Terence G., E-mail: langdon@usc.edu [Materials Research Group, Faculty of Engineering and the Environment, University of Southampton, Southampton SO17 1BJ (United Kingdom); Departments of Aerospace and Mechanical Engineering and Materials Science, University of Southern California, Los Angeles, CA 90089-1453 (United States)

2011-11-15

Aluminum of commercial purity was processed by equal-channel angular pressing (ECAP) through two, four and eight passes at room temperature. A series of [1 1 4] convergent-beam electron diffraction (CBED) zone axis patterns were obtained using an electron probe with a diameter of 20 nm. Observations were recorded both immediately adjacent to the grain boundaries and in the grain interiors. Symmetry breaking of the higher-order Laue zone (HOLZ) lines was observed adjacent to the boundaries after two and four passes but not in the grain interiors. Pattern simulation of the CBED patterns taken from the two- and four-pass samples adjacent to the boundaries revealed a homogeneous strain with compressive and shear components. The presence of these homogeneous strains demonstrates that the internal stresses associated with the deformation of aluminum at room temperature are localized in the close vicinity, to within {approx}20 nm, of the grain boundaries.

Shear strength behavior of geotextile/geomembrane interfaces

Directory of Open Access Journals (Sweden)

Belén M. Bacas

2015-12-01

Full Text Available This paper aims to study the shear interaction mechanism of one of the critical geosynthetic interfaces, the geotextile/geomembrane, typically used for lined containment facilities such as landfills. A large direct shear machine is used to carry out 90 geosynthetic interface tests. The test results show a strain softening behavior with a very small dilatancy (<0.5 mm and nonlinear failure envelopes at a normal stress range of 25–450 kPa. The influences of the micro-level structure of these geosynthetics on the macro-level interface shear behavior are discussed in detail. This study has generated several practical recommendations to help professionals to choose what materials are more adequate. From the three geotextiles tested, the thermally bonded monofilament exhibits the best interface shear strength under high normal stress. For low normal stress, however, needle-punched monofilaments are recommended. For the regular textured geomembranes tested, the space between the asperities is an important factor. The closer these asperities are, the better the result achieves. For the irregular textured geomembranes tested, the nonwoven geotextiles made of monofilaments produce the largest interface shear strength.

Midbroken Reinforced Concrete Shear Frames Due to Earthquakes

DEFF Research Database (Denmark)

Köylüoglu, H. U.; Cakmak, A. S.; Nielsen, Søren R. K.

A non-linear hysteretic model for the response and local damage analyses of reinforced concrete shear frames subject to earthquake excitation is proposed, and, the model is applied to analyse midbroken reinforced concrete (RC) structures due to earthquake loads. Each storey of the shear frame...

Fifty years of shear zones

Science.gov (United States)

Graham, Rodney

2017-04-01

temperature shear zones with flaser gabbro and amphibolitization must have been developed at deeper levels in the shear zone and 'dragged upwards'. An attempt to justify these assertions will made using outcrop exsmples and some deep Seismic data John Ramsay was always cautious about up-scaling and indulging in large scale tectonic speculations, but without his geometric acumen the big scale picture would have been even less clear. Ramsay, J.G. and Graham, R.H., 1970. Strain variation in shear belts. Canadian Journal of Earth Sciences, 7(3), pp.786-813.

Local magnetic shear control in a tokamak via fast wave minority ion current drive: Theory and experiments in JET

International Nuclear Information System (INIS)

Bhatnagar, V.P.; Start, D.F.H.; Jacquinot, J.; Chaland, F.; Cherubini, A.; Porcelli, F.

1994-01-01

When an ion cyclotron resonance heating (ICRH) antenna array is phased (Δ Φ ≠ 0 or π), the excited asymmetric k parallel spectrum can drive non-inductive currents by interaction of fast waves both with electrons (transit time magnetic pumping (e-TTMP) and Landau damping (e-LD)) and with ions at minority (fundamental) or harmonic cyclotron resonances, depending upon the scenario. On the basis of earlier theories, a simplified description is presented that includes the minority ion and electron current drive effects simultaneously in a 3-D ray tracing calculation in the tokamak geometry. The experimental results of sawtooth stabilization or destabilization in JET using the minority ion current drive scheme are presented. This scheme allows a modification of the local current density gradient (or the magnetic shear) at the q = 1 surface resulting in a control of a sawteeth. The predictions of the above model of current drive and its effects on sawtooth period calculated in conjunction with a model of stability of internal resistive kink modes, that encompasses the effects of both the fast particle pressure and the local (q = 1) magnetic shear, are found to be qualitatively in good agreement with the experimental results. Further, the results are discussed of our model of fast wave current drive scenarios of magnetic shear reversal with a view to achieving long duration high confinement regimes in the forthcoming experimental campaign on JET. Finally, the results are presented of minority current drive for sawtooth control in next step devices such as the International Thermonuclear Experimental Reactor (ITER). (author). 44 refs, 23 figs, 3 tabs

Effect of Asymmetric Rolling on Plastic Anisotropy of Low Carbon Steels during Simple Shear Tests

International Nuclear Information System (INIS)

Gracio, J. J.; Vincze, G.; Panigrahi, B. B.; Kim, H. J.; Barlat, F.; Rauch, E. F.; Yoon, J. W.

2010-01-01

Simple shear tests are performed on low carbon steel pre-deformed in conventional, asymmetric and orthogonal-asymmetric rolling. The simple-shear tests were carried out at 0 deg. , 45 deg. and 135 deg. with respect to the previous rolling direction. For a reduction ratio of 15%, a transient stagnation in the hardening rate is observed at reloading for all changes in strain path. The shear stress level, the hardening rate and extent of the plateau appear to be insensitive to the preliminary applied rolling conditions. After a reduction ratio of 50%, plastic instability was detected at reloading for all the changes of strain path and rolling conditions studied. A specific heat treatment was then designed allowing the material to become ductile after rolling while retaining the fine microstructure and therefore the high strength. Promising results were obtained essentially for 45 deg. shear tests.

Shear Strengthening of RC Beams Using Sprayed Glass Fiber Reinforced Polymer

Directory of Open Access Journals (Sweden)

Sayed Mohamad Soleimani

2012-01-01

Full Text Available The effectiveness of externally bonded sprayed glass fiber reinforced polymer (Sprayed GFRP in shear strengthening of RC beams under quasi-static loading is investigated. Different techniques were utilized to enhance the bond between concrete and Sprayed GFRP, involving the use of through bolts and nuts paired with concrete surface preparation through sandblasting and through the use of a pneumatic chisel prior to Sprayed GFRP application. It was found that roughening the concrete surface using a pneumatic chisel and using through bolts and nuts were the most effective techniques. Also, Sprayed GFRP applied on 3 sides (U-shaped was found to be more effective than 2-sided Sprayed GFRP in shear strengthening. Sprayed GFRP increased the shear load-carrying capacity and energy absorption capacities of RC beams. It was found that the load-carrying capacity of strengthened RC beams was related to an effective strain of applied Sprayed GFRP. This strain was related to Sprayed GFRP configuration and the technique used to enhance the concrete-FRP bond. Finally, an equation was proposed to calculate the contribution of Sprayed GFRP in the shear strength of an RC beam.

Novel Approach for Prediction of Localized Necking in Case of Nonlinear Strain Paths

Science.gov (United States)

Drotleff, K.; Liewald, M.

2017-09-01

Rising customer expectations regarding design complexity and weight reduction of sheet metal components alongside with further reduced time to market implicate increased demand for process validation using numerical forming simulation. Formability prediction though often is still based on the forming limit diagram first presented in the 1960s. Despite many drawbacks in case of nonlinear strain paths and major advances in research in the recent years, the forming limit curve (FLC) is still one of the most commonly used criteria for assessing formability of sheet metal materials. Especially when forming complex part geometries nonlinear strain paths may occur, which cannot be predicted using the conventional FLC-Concept. In this paper a novel approach for calculation of FLCs for nonlinear strain paths is presented. Combining an interesting approach for prediction of FLC using tensile test data and IFU-FLC-Criterion a model for prediction of localized necking for nonlinear strain paths can be derived. Presented model is purely based on experimental tensile test data making it easy to calibrate for any given material. Resulting prediction of localized necking is validated using an experimental deep drawing specimen made of AA6014 material having a sheet thickness of 1.04 mm. The results are compared to IFU-FLC-Criterion based on data of pre-stretched Nakajima specimen.

Hoof position during limb loading affects dorsoproximal bone strains on the equine proximal phalanx.

Science.gov (United States)

Singer, Ellen; Garcia, Tanya; Stover, Susan

2015-07-16

Sagittal fractures of the proximal phalanx (P1) in the racehorse appear to be associated with turf racing surfaces, which are known to restrict forward slide of the foot at impact. We hypothesized that restriction of forward foot slip would result in higher P1 bone strains during metacarpophalangeal joint (MCPJ) hyperextension. Unilateral limbs from six equine cadavers were instrumented with strain gauges and bone reference markers to measure dorsoproximal P1 bone strains and MCPJ extension, collateromotion and axial rotation during in vitro limb loading to 10,500 N. By limiting movement of the distal actuator platform, three different foot conditions (forward, free, and restricted) were applied in a randomised block design. Bone reference markers, recorded by video, were analyzed to determine motion of P1 relative to MC3. Rosette strain data were reduced to principal and shear magnitudes and directions. A mixed model ANOVA determined the effect of foot position on P1 bone strains and MCPJ angles. At 10,000 N load, the restricted condition resulted in higher P1 axial compressive (p=0.015), maximum shear (p=0.043) and engineering shear (p=0.046) strains compared to the forward condition. The restricted condition had higher compressive (p=0.025) and lower tensile (p=0.043) principal strains compared to the free condition. For the same magnitude of principal or shear strains, axial rotation and collateromotion angles were greatest for the restricted condition. Therefore, the increase in P1 principal compressive and shear bone strains associated with restricted foot slip indicate that alterations in foot:ground interaction may play a role in fracture occurrence in horses. Copyright © 2015 Elsevier Ltd. All rights reserved.

Ab initio study of Ni2MnGa under shear deformation

Directory of Open Access Journals (Sweden)

Zelený Martin

2015-01-01

Full Text Available The effect of shear deformation on Ni2MnGa magnetic shape memory alloy has been investigated using ab initio electronic structure calculations. We used the projector-augmented wave method for the calculations of total energies and stresses as functions of applied affine shear deformation. The studied nonmodulated martensite (NM phase exhibits a tetragonally distorted L21 structure with c/a > 1. A large strain corresponding to simple shears in {001}, {100} and {100} systems was applied to describe a full path between two equivalent NM lattices. We also studied {101} shear which is related to twining of NM phase. Twin reorientation in this system is possible, because applied positive shear results in path with significantly smaller energetic barrier than for negative shear and for shears in other studied systems. When the full relaxation of lattice parameters is allowed, the barriers further strongly decrease and the structures along the twinning path can be considered as orthorhombic.

Effects of local film properties on the nucleation and growth of tin whiskers and hillocks

Science.gov (United States)

Sarobol, Pylin

Whiskers and hillocks grow spontaneously on Pb-free Sn electrodeposited films as a response to thin film stresses. Stress relaxation occurs by atom deposition to specific grain boundaries in the plane of the film, with hillocks being formed when grain boundary migration accompanies growth out of the plane of the film. The implication for whisker formation in electronics is serious: whiskers can grow to be millimeters long, sometimes causing short circuiting between adjacent components and, thereby, posing serious electrical reliability risks. In order to develop more effective whisker mitigation strategies, a predictive physics-based model has been needed. A growth model is developed, based on grain boundary faceting, localized Coble creep, as well as grain boundary sliding for whiskers, and grain boundary sliding with shear induced grain boundary migration for hillocks. In this model of whisker formation, two mechanisms are important: accretion of atoms by Coble creep on grain boundary planes normal to the growth direction inducing a grain boundary shear and grain boundary sliding in the direction of whisker growth. The model accurately captures the importance of the geometry of "surface grains"---shallow grains on film surfaces whose depths are significantly less than their in-plane grain sizes. A critical factor in the analysis is the ratio of the grain boundary sliding coefficient to the in-plane film compressive stress. If the accretion-induced shear stresses are not coupled to grain boundary motion and sliding occurs, a whisker forms. If the shear stress is coupled to grain boundary migration, a hillock forms. Based on this model, long whiskers grow from shallow surface grains with easy grain boundary sliding in the direction of growth. Other observed growth morphologies will be discussed in light of our model. Additional insights into the preferred sites for whisker and hillock growth were developed based on elastic anisotropy, local film microstructure

Frictional processes in smectite-rich gouges sheared at slow to high slip rates

Science.gov (United States)

Aretusini, Stefano; Mittempergher, Silvia; Gualtieri, Alessandro; Di Toro, Giulio

2015-04-01

.02 (slip-strengthening behavior), (2) for V = 0.1 m/s velocity and slip neutral (μi = μss = 0.77±0.02) and (3) for V ≥ 0.3 m/s the friction coefficient was velocity and slip weakening with μss = 0.32±0.02 for V = 1.5 m/s. The Rietveld analysis of the smectite-rich standard endmember showed (1) the insensitivity of the amount of the amorphous fraction with frictional work and (2) the shift and broadening of both the (001) and (110) peaks of Ca-montmorillonite with increasing frictional work (i.e., product of shear stress with slip, here from 5.2 Jm-2 to 11.8 Jm-2). Instead, mineralogical and lattice changes were unrelated to the frictional work rate (i.e., product of shear stress with slip rate). Strain localization in the gouge layer was observed for V ≥ 0.3 m/s (SEM investigations); for V < 0.3 m/s, strain was distributed and the gouge layer pervasively foliated. We conclude that the degree of amorphization of the sheared gouges was not responsible of the measured frictional weakening; instead, weakening was concomitant to strain localization.

Rotation of small clusters in sheared metallic glasses

International Nuclear Information System (INIS)

Delogu, Francesco

2011-01-01

Graphical abstract: When a Cu 50 Ti 50 metallic glass is shear-deformed, the irreversible rearrangement of local structures allows the rigid body rotation of clusters. Highlights: → A shear-deformed Cu 50 Ti 50 metallic glass was studied by molecular dynamics. → Atomic displacements occur at irreversible rearrangements of local structures. → The dynamics of such events includes the rigid body rotation of clusters. → Relatively large clusters can undergo two or more complete rotations. - Abstract: Molecular dynamics methods were used to simulate the response of a Cu 50 Ti 50 metallic glass to shear deformation. Attention was focused on the atomic displacements taking place during the irreversible rearrangement of local atomic structures. It is shown that the apparently disordered dynamics of such events hides the rigid body rotation of small clusters. Cluster rotation was investigated by evaluating rotation angle, axis and lifetimes. This permitted to point out that relatively large clusters can undergo two or more complete rotations.

In-situ measurement of texture and elastic strains with HIPPO-CRATES

International Nuclear Information System (INIS)

Hartig, Ch.; Vogel, S.C.; Mecking, H.

2006-01-01

In this paper, the micromechanical interaction between constituents of a metallic material during elastic and plastic deformation are analyzed by comparing experimental results with modeling predictions. This comparison aims at determining the locally acting internal stresses, the spatial distribution of strains and the rules allowing deriving the macroscopic behavior of the material from the behavior of its microscopic constituents. We report the application of a new deformation apparatus CRATES, which allows measuring texture and crystal lattice spacings, and from these crystal lattice strains, using neutron diffraction. From the in-situ measured elastic lattice strains ε hkl the corresponding local stresses can be derived. The deformation apparatus allows uni-axial tensile or compressive deformation up to 100 kN and is specifically designed for use in the HIPPO neutron time-of-flight diffractometer. In this paper, we report initial results on an iron-copper model system (Fe100, Fe33Cu67, Fe67Cu33, vol.%) and commercial magnesium alloys (Mg-AZ31 and Mg-AZ80). Finite element calculations using a crystal-plastic constitutive law, allowing for shear and hardening of crystallographic slip-systems, were used for the interpretation of the measurements

A fiber optic strain measurement and quench localization for use in superconducting accelerator dipole magnets

International Nuclear Information System (INIS)

van Oort, J.M.; Scanlan, R.M.; ten Kate, H.H.J.

1994-01-01

A novel fiber-optic measurement system for superconducting accelerator magnets is described. The principal component is an extrinsic Fabry-Perot Interferometer to determine localized strain and stress in coil windings. The system can be used either as a sensitive relative strain measurement system or as an absolute strain detector. Combined, one can monitor the mechanical behaviour of the magnet system over time during construction, long time storage and operation. The sensing mechanism is described, together with various tests in laboratory environments. The test results of a multichannel test matrix to be incorporated first in the dummy coils and then in the final version of a 13T Nb 3 Sn accelerator dipole magnet are presented. Finally, the possible use of this system as a quench localization system is proposed

Reversed shear Alfven eigenmode stabilization by localized electron cyclotron heating

Energy Technology Data Exchange (ETDEWEB)

Van Zeeland, M A; Hyatt, A W; Lohr, J; Petty, C C [General Atomics, PO Box 85608 San Diego, CA 92186-5608 (United States); Heidbrink, W W [University of California-Irvine, Irvine, CA 92697 (United States); Nazikian, R; Solomon, W M; Gorelenkov, N N; Kramer, G J [Princeton Plasma Physics Laboratory, Princeton, NJ 08543-0451 (United States); Austin, M E [University of Texas-Austin, Austin, TX 78712 (United States); Berk, H L [Institute for Fusion Studies, University of Texas at Austin, Austin, TX 78712 (United States); Holcomb, C T; Makowski, M A [Lawrence Livermore National Laboratory, Livermore, CA (United States); McKee, G R [University of Wisconsin-Madison, Madison, WI 53726 (United States); Sharapov, S E [Euratom/UKAEA Fusion Association, Culham, Abingdon, Oxfordshire, OX14 3DB (United Kingdom); Rhodes, T L [University of California-Los Angeles, Los Angeles, California, 90095 (United States)], E-mail: vanzeeland@fusion.gat.com

2008-03-15

Reversed shear Alfven eigenmode (RSAE) activity in DIII-D is stabilized by electron cyclotron heating (ECH) applied near the minimum of the magnetic safety factor (q{sub min}) in neutral beam heated discharges with reversed-magnetic shear. The degree of RSAE stabilization, fast ion density and the volume averaged neutron production (S{sub n}) are highly dependent on ECH deposition location relative to q{sub min}. While discharges with ECH stabilization of RSAEs have higher S{sub n} and more peaked fast ion profiles than discharges with significant RSAE activity, neutron production remains strongly reduced (up to 60% relative to TRANSP predictions assuming classical fast ion transport) even when RSAEs are stabilized.

Comparison of shear wave velocity measurements assessed with two different ultrasound systems in an ex-vivo tendon strain phantom.

Science.gov (United States)

Rosskopf, Andrea B; Bachmann, Elias; Snedeker, Jess G; Pfirrmann, Christian W A; Buck, Florian M

2016-11-01

The purpose of this study is to compare the reliability of SW velocity measurements of two different ultrasound systems and their correlation with the tangent traction modulus in a non-static tendon strain model. A bovine tendon was fixed in a custom-made stretching device. Force was applied increasing from 0 up to 18 Newton. During each strain state the tangent traction modulus was determined by the stretcher device, and SW velocity (m/s) measurements using a Siemens S3000 and a Supersonic Aixplorer US machine were done for shear modulus (kPa) calculation. A strong significant positive correlation was found between SW velocity assessed by the two ultrasound systems and the tangent traction modulus (r = 0.827-0.954, p Aixplorer 0.25 ± 0.3 m/s (p = 0.034). Mean difference of SW velocity between the two US-systems was 0.37 ± 0.3 m/s (p = 0.012). In conclusion, SW velocities are highly dependent on mechanical forces in the tendon tissue, but for controlled mechanical loads appear to yield reproducible and comparable measurements using different US systems.

Shear zones between rock units with no relative movement

DEFF Research Database (Denmark)

Koyi, Hemin; Schmeling, Harro; Burchardt, Steffi

2013-01-01

Shear zones are normally viewed as relatively narrow deformation zones that accommodate relative displacement between two "blocks" that have moved past each other in opposite directions. This study reports localized zones of shear between adjacent blocks that have not moved past each other. Such ...... given credit for and may be responsible for some reverse kinematics reported in shear zones....... or wakes, elongated bodies (vertical plates or horizontal rod-like bodies) produce tabular shear zones or wakes. Unlike conventional shear zones across which shear indicators usually display consistent symmetries, shear indicators on either side of the shear zone or wake reported here show reverse...... kinematics. Thus profiles exhibit shear zones with opposed senses of movement across their center-lines or -planes.We have used field observations and results from analytical and numerical models to suggest that examples of wakes are the transit paths that develop where denser blocks sink within salt...

Amorphization and Frictional Processes in Smectite-Quartz Gouge Mixtures Sheared from Sub-seismic to Seismic Slip Rates

Science.gov (United States)

Aretusini, S.; Mittempergher, S.; Spagnuolo, E.; Di Toro, G.; Gualtieri, A.; Plümper, O.

2015-12-01

Slipping zones in shallow sections of megathrusts and large landslides are often made of smectite and quartz gouge mixtures. Experiments aimed at investigating the frictional processes operating at high slip rates (>1 m/s) may unravel the mechanics of these natural phenomena. Here we present a new dataset obtained with two rotary shear apparatus (ROSA, Padua University; SHIVA, INGV-Rome). Experiments were performed at room humidity and temperature on four mixtures of smectite (Ca-Montmorillonite) and quartz with 68, 50, 25, 0 wt% of smectite. The gouges were slid for 3 m at normal stress of 5 MPa and slip rate V from 300 µm/s to 1.5 m/s. Temperature during the experiments was monitored with four thermocouples and modeled with COMSOL Multiphysics. In smectite-rich mixtures, the friction coefficient µ evolved with slip according to three slip rate regimes: in regime 1 (V0.3 m/s) µ had strong slip-weakening behavior. Instead, in quartz-rich mixtures the gouge had a monotonic slip-weakening behavior, independently of V. Temperature modelling showed that the fraction of work rate converted into heat decreased with increasing smectite content and slip rate. Quantitative X-ray powder diffraction (Rietveld method) indicates that the production of amorphous material from smectite breakdown increased with frictional work but was independent of work rate. Scanning Electron Microscopy investigation evidenced strain localization and presence of dehydrated clays for V≥0.3 m/s; instead, for V<0.3 m/s, strain was distributed and the gouge layer pervasively foliated. In conclusion, amorphization of the sheared gouges was not responsible of the measured frictional weakening. Instead, slip-weakening was concomitant to strain localization and possible vaporization of water adsorbed on smectite grain surfaces.

Bolt Shear Force Sensor

Science.gov (United States)

2015-03-12

0030] FIG. 7 is an isometric view of a deformable ring of the bolt shear force sensor of the present invention with an optical Attorney Docket No...102587 9 of 19 fiber having Bragg gratings wound around the ring; [0031] FIG. 8 is an isometric view of the deformable ring with wire strain... strength . [0047] Once the joint is subjected to an external load (see force arrows “F” and “F/2”); any frictional resistance to slip is overcome and

Mechanical characteristics under monotonic and cyclic simple shear of spark plasma sintered ultrafine-grained nickel

International Nuclear Information System (INIS)

Dirras, G.; Bouvier, S.; Gubicza, J.; Hasni, B.; Szilagyi, T.

2009-01-01

The present work focuses on understanding the mechanical behavior of bulk ultrafine-grained nickel specimens processed by spark plasma sintering of high purity nickel nanopowder and subsequently deformed under large amplitude monotonic simple shear tests and strain-controlled cyclic simple shear tests at room temperature. During cyclic tests, the samples were deformed up to an accumulated von Mises strain of about ε VM = 0.75 (the flow stress was in the 650-700 MPa range), which is extremely high in comparison with the low tensile/compression ductility of this class of materials at quasi-static conditions. The underlying physical mechanisms were investigated by electron microscopy and X-ray diffraction profile analysis. Lattice dislocation-based plasticity leading to cell formation and dislocation interactions with twin boundaries contributed to the work-hardening of these materials. The large amount of plastic strain that has been reached during the shear tests highlights intrinsic mechanical characteristics of the ultrafine-grained nickel studied here.

Mechanical characteristics under monotonic and cyclic simple shear of spark plasma sintered ultrafine-grained nickel

Energy Technology Data Exchange (ETDEWEB)

Dirras, G., E-mail: dirras@univ-paris13.fr [LPMTM - CNRS, Institut Galilee, Universite Paris 13, 99 Avenue J.B. Clement, 93430 Villetaneuse (France); Bouvier, S. [LPMTM - CNRS, Institut Galilee, Universite Paris 13, 99 Avenue J.B. Clement, 93430 Villetaneuse (France); Gubicza, J. [Department of Materials Physics, Eoetvoes Lorand University, P.O.B. 32, Budapest H-1518 (Hungary); Hasni, B. [LPMTM - CNRS, Institut Galilee, Universite Paris 13, 99 Avenue J.B. Clement, 93430 Villetaneuse (France); Szilagyi, T. [Department of Materials Physics, Eoetvoes Lorand University, P.O.B. 32, Budapest H-1518 (Hungary)

2009-11-25

The present work focuses on understanding the mechanical behavior of bulk ultrafine-grained nickel specimens processed by spark plasma sintering of high purity nickel nanopowder and subsequently deformed under large amplitude monotonic simple shear tests and strain-controlled cyclic simple shear tests at room temperature. During cyclic tests, the samples were deformed up to an accumulated von Mises strain of about {epsilon}{sub VM} = 0.75 (the flow stress was in the 650-700 MPa range), which is extremely high in comparison with the low tensile/compression ductility of this class of materials at quasi-static conditions. The underlying physical mechanisms were investigated by electron microscopy and X-ray diffraction profile analysis. Lattice dislocation-based plasticity leading to cell formation and dislocation interactions with twin boundaries contributed to the work-hardening of these materials. The large amount of plastic strain that has been reached during the shear tests highlights intrinsic mechanical characteristics of the ultrafine-grained nickel studied here.

Synchrotron measurements of local microstructure and residual strains in ductile cast iron

DEFF Research Database (Denmark)

Zhang, Yubin; Andriollo, Tito; Fæster, Søren

2017-01-01

The local microstructure and distribution of thermally induced residual strains in ferrite matrix grains around an individual spherical graphite nodule in ductile cast iron (DCI) were measured using a synchrotron X-ray micro-diffraction technique. It is found that the matrix grains are deformed...

Effect of single-particle magnetostriction on the shear modulus of compliant magnetoactive elastomers

Science.gov (United States)

Kalita, Viktor M.; Snarskii, Andrei A.; Shamonin, Mikhail; Zorinets, Denis

2017-03-01

The influence of an external magnetic field on the static shear strain and the effective shear modulus of a magnetoactive elastomer (MAE) is studied theoretically in the framework of a recently introduced approach to the single-particle magnetostriction mechanism [V. M. Kalita et al., Phys. Rev. E 93, 062503 (2016), 10.1103/PhysRevE.93.062503]. The planar problem of magnetostriction in an MAE with magnetically soft inclusions in the form of a thin disk (platelet) having the magnetic anisotropy in the plane of this disk is solved analytically. An external magnetic field acts with torques on magnetic filler particles, creates mechanical stresses in the vicinity of inclusions, induces shear strain, and increases the effective shear modulus of these composite materials. It is shown that the largest effect of the magnetic field on the effective shear modulus should be expected in MAEs with soft elastomer matrices, where the shear modulus of the matrix is less than the magnetic anisotropy constant of inclusions. It is derived that the effective shear modulus is nonlinearly dependent on the external magnetic field and approaches the saturation value in magnetic fields exceeding the field of particle anisotropy. It is shown that model calculations of the effective shear modulus correspond to a phenomenological definition of effective elastic moduli and magnetoelastic coupling constants. The obtained theoretical results compare well with known experimental data. Determination of effective elastic coefficients in MAEs and their dependence on magnetic field is discussed. The concentration dependence of the effective shear modulus at higher filler concentrations has been estimated using the method of Padé approximants, which predicts that both the absolute and relative changes of the magnetic-field-dependent effective shear modulus will significantly increase with the growing concentration of filler particles.

Microstructure and texture development during high-strain torsion of NiAl

Energy Technology Data Exchange (ETDEWEB)

Kloeden, B.

2006-07-01

In this study polycrystalline NiAl has been subjected to torsion deformation. The deformation, microstructure and texture development subject to the shear strain are studied by different techniques (Electron Back-Scatter and High Energy Synchrotron Radiation). Beside the development of microstructure and texture with shear strain, the effect of an initial texture as well as the deformation temperature on the development of texture and microstructure constitute an important part of this study. Therefore, samples with three different initial textures were deformed in the temperature range T=700 K-1300 K. The shear stress-shear strain curves are characterized by a peak at low strains, which is followed by softening and a steady state at high strains. Grain refinement takes place for all samples and the average grain size decreases with temperature. For temperatures T>1000 K, discontinuous dynamic recrystallization occurs, by which new grains form by nucleation and subsequent growth. The texture is characterized by two components, {l_brace}100{r_brace}<100> (cube,C) and {l_brace}110{r_brace}<100> (Goss,G). Torsional creep of NiAl is characterized by a stress exponent, which depends on temperature and an activation energy, which is stress dependent. The Swift effect, due to which samples change their axial dimension during torsion without applied axial stress, is observed for NiAl. (orig.)

Characterization of Shear Properties for APO/MBI Syntactic Foam

Energy Technology Data Exchange (ETDEWEB)

Reser, Patrick M. [Univ. of New Mexico, Albuquerque, NM (United States); Lewis, Matthew W. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Clark, Jarod [Univ. of New Mexico, Albuquerque, NM (United States); Ahuja, Nishant [Univ. of New Mexico, Albuquerque, NM (United States); Lenke, Lary R. [Univ. of New Mexico, Albuquerque, NM (United States)

2017-12-14

their procedures are discussed in Chapter 2. Chapter 2 contains the types of tests performed and the apparatus used for testing the material. Chapter 2 also has a brief explanation of the equipment and the procedures used for conducting the tests. In Chapter 3, the material characteristics and mechanical properties obtained from the tests are described; composite plots of deviatoric vs. mean stress and deviatoric stress vs. longitudinal strain are also included. The plots of deviatoric stress vs. mean stress clearly identify the shear envelope for the material. Chapter 4 summarizes the vital information obtained from the tests and the conclusions made. All the necessary plots and the data generated during the testing have been included in the Appendix. The information in the appendix includes plots of: Strain vs. Time, Stress vs. Time, Stress vs. Strain, Mean Stress vs. Volumetric Strain, Lateral Strain vs. Longitudinal Strain, and q vs. p. Bulk modulus, Poisson’s ratio, and Young’s modulus are displayed in the appropriate plots in each appendix.

A fiber-optic strain measurement and quench localization system for use in superconducting accelerator dipole magnets

NARCIS (Netherlands)

van Oort, J.M.; Scanlan, Ronald M.; ten Kate, Herman H.J.

1995-01-01

A novel fiber-optic measurement system for superconducting accelerator magnets is described. The principal component is an extrinsic Fabry-Perot interferometer to determine localized strain and stress in coil windings. The system can be used either as a sensitive relative strain measurement system

Molecular characteristics of stress overshoot for polymer melts under start-up shear flow.

Science.gov (United States)

Jeong, Sohdam; Kim, Jun Mo; Baig, Chunggi

2017-12-21

Stress overshoot is one of the most important nonlinear rheological phenomena exhibited by polymeric liquids undergoing start-up shear at sufficient flow strengths. Despite considerable previous research, the fundamental molecular characteristics underlying stress overshoot remain unknown. Here, we analyze the intrinsic molecular mechanisms behind the overshoot phenomenon using atomistic nonequilibrium molecular dynamics simulations of entangled linear polyethylene melts under shear flow. Through a detailed analysis of the transient rotational chain dynamics, we identify an intermolecular collision angular regime in the vicinity of the chain orientation angle θ ≈ 20° with respect to the flow direction. The shear stress overshoot occurs via strong intermolecular collisions between chains in the collision regime at θ = 15°-25°, corresponding to a peak strain of 2-4, which is an experimentally well-known value. The normal stress overshoot appears at approximately θ = 10°, at a corresponding peak strain roughly equivalent to twice that for the shear stress. We provide plausible answers to several basic questions regarding the stress overshoot, which may further help understand other nonlinear phenomena of polymeric systems.

Development of Test Method for Simple Shear and Prediction of Hardening Behavior Considering the Branchings Effect

International Nuclear Information System (INIS)

Kim, Dongwook; Bang, Sungsik; Kim, Minsoo; Lee, Hyungyil; Kim, Naksoo

2013-01-01

In this study we establish a process to predict hardening behavior considering the Branchings effect for zircaloy-4 sheets. When a metal is compressed after tension in forming, the yield strength decreases. For this reason, the Branchings effect should be considered in FE simulations of spring-back. We suggested a suitable specimen size and a method for determining the optimum tightening torque for simple shear tests. Shear stress-strain curves are obtained for five materials. We developed a method to convert the shear load-displacement curve to the effective stress-strain curve with Fea. We simulated the simple shear forward/reverse test using the combined isotropic/kinematic hardening model. We also investigated the change of the load-displacement curve by varying the hardening coefficients. We determined the hardening coefficients so that they follow the hardening behavior of zircaloy-4 in experiments

Development of Test Method for Simple Shear and Prediction of Hardening Behavior Considering the Branchings Effect

Energy Technology Data Exchange (ETDEWEB)

Kim, Dongwook; Bang, Sungsik; Kim, Minsoo; Lee, Hyungyil; Kim, Naksoo [Sogang Univ., Seoul (Korea, Republic of)

2013-10-15

In this study we establish a process to predict hardening behavior considering the Branchings effect for zircaloy-4 sheets. When a metal is compressed after tension in forming, the yield strength decreases. For this reason, the Branchings effect should be considered in FE simulations of spring-back. We suggested a suitable specimen size and a method for determining the optimum tightening torque for simple shear tests. Shear stress-strain curves are obtained for five materials. We developed a method to convert the shear load-displacement curve to the effective stress-strain curve with Fea. We simulated the simple shear forward/reverse test using the combined isotropic/kinematic hardening model. We also investigated the change of the load-displacement curve by varying the hardening coefficients. We determined the hardening coefficients so that they follow the hardening behavior of zircaloy-4 in experiments.

A numerical model for adiabatic shear bands with application to a thick-walled cylinder in 304 stainless steel

International Nuclear Information System (INIS)

Liu, Mingtao; Li, Yongchi; Hu, Xiuzhang; Hu, Haibo

2014-01-01

The formation of an adiabatic shear band (ASB) experiences three stages: stable plastic flow, nucleation and a fluid-like stage. For different stages, the microstructures of the material undergo great changes. The mechanical behavior of the material in each stage has its own unique characteristics. To describe these characteristics, a multi-stage model for the shear band is proposed. For the stable plastic flow stage, a modified adiabatic J–C constitutive relationship is used. For the nucleation stage, the effects of work hardening and temperature softening are described by a power function of plastic strain. A Newtonian fluid model is used for the fluid-like stage. The formation of a shear band is an instability process. Various defects in the material are perturbation sources, which change the local yield stress. To describe the disturbances, a probability factor is introduced into the macroscopic constitutive relationship. The yield stress in the material is assumed to obey a Gaussian distribution. The multi-stage model combined with a probability factor is applied to simulate the rupture of thick-walled cylinder in 304 Stainless Steel (304SS). A close agreement is found between the simulation and experimental results, such as the failure mechanism, shear band spacing and propagating velocity of the shear band. By combining the experimental results with the simulation results, the importance of the nucleation stage is emphasized. (paper)

On transformation shear of precipitated zirconia particles

International Nuclear Information System (INIS)

Zhang, J.M.; Lam, K.Y.

1993-01-01

A model is proposed to investigate the transformation shear of the precipitated zirconia particles which undergo a stress-induced lattice transformation from tetragonal to monoclinic symmetry. Kinematically admissible twinning planes and the corresponding twinning elements are determined according to the continuum theory of dispacive phase transformation. It is postulated that only one twinning mode prevails in each transformed particle and that the minimization of elastic strain energy change dictates the morphology of the transformed variants. The transformation shear is determined by the twinning mode and the volume fraction of the corresponding variant. Numerical calculations show that each of the six kinematically admissible twinning modes may be kinematically favorable and therefore operate in constrained particle. The actual transformation shear in a transformed particle is shown to be dependent on the transformation stress, on the particle shape as well as on the lattice orientation relative to the principal axes of the ellipsoidal particle

Nonlinear Simulations of Trapped Electron Mode Turbulence in Low Magnetic Shear Stellarators

Science.gov (United States)

Faber, B. J.; Pueschel, M. J.; Terry, P. W.; Hegna, C. C.

2017-10-01

Optimized stellarators, like the Helically Symmetric eXperiment (HSX), often operate with small global magnetic shear to avoid low-order rational surfaces and magnetic islands. Nonlinear, flux-tube gyrokinetic simulations of density-gradient-driven Trapped Electron Mode (TEM) turbulence in HSX shows two distinct spectral fluctuation regions: long-wavelength slab-like TEMs localized by global magnetic shear that extend along field lines and short-wavelength TEMs localized by local magnetic shear to a single helical bad curvature region. The slab-like TEMs require computational domains significantly larger than one poloidal turn and are computationally expensive, making turbulent optimization studies challenging. A computationally more efficient, zero-average-magnetic-shear approximation is shown to sufficiently describe the relevant nonlinear physics and replicate finite-shear computations, and can be exploited in quasilinear models based on linear gyrokinetics as a feasible optimization tool. TEM quasilinear heat fluxes are computed with the zero-shear approximation and compared to experimentally-relevant nonlinear gyrokinetic TEM heat fluxes for HSX. Research supported by U.S. DoE Grants DE-FG02-99ER54546, DE-FG02-93ER54222 and DE-FG02-89ER53291.

Physics of Transitional Shear Flows Instability and Laminar–Turbulent Transition in Incompressible Near-Wall Shear Layers

CERN Document Server

Boiko, Andrey V; Grek, Genrih R; Kozlov, Victor V

2012-01-01

Starting from fundamentals of classical stability theory, an overview is given of the transition phenomena in subsonic, wall-bounded shear flows. At first, the consideration focuses on elementary small-amplitude velocity perturbations of laminar shear layers, i.e. instability waves, in the simplest canonical configurations of a plane channel flow and a flat-plate boundary layer. Then the linear stability problem is expanded to include the effects of pressure gradients, flow curvature, boundary-layer separation, wall compliance, etc. related to applications. Beyond the amplification of instability waves is the non-modal growth of local stationary and non-stationary shear flow perturbations which are discussed as well. The volume continues with the key aspect of the transition process, that is, receptivity of convectively unstable shear layers to external perturbations, summarizing main paths of the excitation of laminar flow disturbances. The remainder of the book addresses the instability phenomena found at l...

Identifikasi Brucella abortus Isolat Lokal dengan Brucella abortus Strain Specific-Polymerase Chain Reaction (IDENTIFICATION OF LOCAL ISOLATES OF BRUCELLA ABORTUS USING BRUCELLA ABORTUS STRAIN SPECIFIC-POLYMERASE CHAIN REACTION ASSAY

Directory of Open Access Journals (Sweden)

Susan Maphilindawati Noor

2014-10-01

Full Text Available Brucella abortus Strain Specific-Polymerase Chain Reaction (BaSS-PCR is a single multiplex PCRtechnique which able to identify and differentiate between Brucella abortus field strains (biovar 1, 2, and4, B. abortus vaccine strains, Brucella species, and non-Brucella species. In this study, BaSS-PCR wasapplied to identify local isolates of B. abortus in order to investigate the B. abortus strains that infectedcattle in Indonesia. Fifty local strains of B.abortus isolated from infected cattle in Java (Jakarta andBandung, South Sulawesi (Maros, East Nusa Tenggara (Kupang and Belu were used in this study. TheDNA bands were observed by agarose gel in the presence of ethidium bromide. Identification was performedbased on the size and number of DNA products amplified by PCR from each isolates. The results showedthat the 50 isolates were of B. abortus field strains. This finding showed that the cause of bovine brucellosisin Indonesia is B. abortus field strains.

Shear flows at the tokamak edge and their interaction with edge-localized modes

International Nuclear Information System (INIS)

Aydemir, A. Y.

2007-01-01

Shear flows in the scrape-off layer (SOL) and the edge pedestal region of tokamaks are shown to arise naturally out of transport processes in a magnetohydrodynamic model. In quasi-steady-state conditions, collisional resistivity coupled with a simple bootstrap current model necessarily leads to poloidal and toroidal flows, mainly localized to the edge and SOL. The role of these flows in the grad-B drift direction dependence of the power threshold for the L (low) to H (high) transition, and their effect on core rotation, are discussed. Theoretical predictions based on symmetries of the underlying equations, coupled with computational results, are found to be in agreement with observations in Alcator C-Mod [Phys. Plasmas 12, 056111 (2005)]. The effects of these self-consistent flows on linear peeling/ballooning modes and their nonlinear consequences are also examined

Combined shearing interferometer and hartmann wavefront sensor

International Nuclear Information System (INIS)

Hutchin, R. A.

1985-01-01

A sensitive wavefront sensor combining attributes of both a Hartmann type of wavefront sensor and an AC shearing interferometer type of wavefront sensor. An incident wavefront, the slope of which is to be detected, is focussed to first and second focal points at which first and second diffraction gratings are positioned to shear and modulate the wavefront, which then diverges therefrom. The diffraction patterns of the first and second gratings are positioned substantially orthogonal to each other to shear the wavefront in two directions to produce two dimensional wavefront slope data for the AC shearing interferometer portion of the wavefront sensor. First and second dividing optical systems are positioned in the two diverging wavefronts to divide the sheared wavefront into an array of subapertures and also to focus the wavefront in each subaperture to a focal point. A quadrant detector is provided for each subaperture to detect the position of the focal point therein, which provides a first indication, in the manner of a Hartmann wavefront sensor, of the local wavefront slope in each subaperture. The total radiation in each subaperture, as modulated by the diffraction grating, is also detected by the quadrant detector which produces a modulated output signal representative thereof, the phase of which relative to modulation by the diffraction grating provides a second indication of the local wavefront slope in each subaperture, in the manner of an AC shearing interferometer wavefront sensor. The data from both types of sensors is then combined by long term averaging thereof to provide an extremely sensitive wavefront sensor

Model shear tests of canisters with smectite clay envelopes in deposition holes

International Nuclear Information System (INIS)

Boergesson, L.

1986-01-01

The consequences of rock displacement across a deposition hole has been investigated by some model tests. The model was scaled 1:10 to a real deposition hole. It was filled with a canister made of solid copper surrounded by highly compacted water saturated MX-80 bentonite. Before shear the swelling pressure was measured by six transducers in order to follow the water uptake process. During shear, pressure, strain, force and deformation were measured in altogether 18 points. The shearing was made at different rates in the various tests. An extensive sampling after shear was made through which the density, water content, degree of saturation, homogenization and the effect of shear on the bentonite and canister could be studied. One important conlusion from these tests was that the rate dependence is about 10% increased shear resistance per decade increased rate of shear. This resulted also in a very clear increase in strain in the canister with increased rate. The results also showed that the saturated bentonite has excellent stress distributing properties and that there is no risk of destroying the canister if the rock displacement is smaller than the thickness of the bentonite cover. The high density of the clay makes the bentonite produce such a high swelling pressure that the material will be very stiff. In the case of a larger shear deformation corresponding to ≅ 50% of the bentonite thickness the result will be a rather large deformation of the canister. A lower density would be preferable if it can be accepted with respect to other required isolating properties. The results also showed that three-dimensional FEM calculation using non-linear material properties is necessary to simulate the shear process. The rate dependence may be taken into account by adapting the properties to the actual rate of shear but might in a later stage be included in the model by giving the material viscous properties. (orig./HP)

A new dedicated finite element for push-over analysis of reinforced concrete shear wall systems

Directory of Open Access Journals (Sweden)

Delal Doğru ORMANCI

2016-06-01

Full Text Available In this study, a finite element which has been analyzed based on anisotropic behavior of reinforced shear walls is developed. Element stiffness matrices were varied based on whether the element is in the tension or the compression zone of the cross-section. Nonlinear behavior of reinforced shear wall model is investigated under horizontal loads. This behavior is defined with a similar approach to plastic hinge assumption in frame structures that the finite element behaves lineer elastic between joints and plastic deformations are concentrated on joints as vertical plastic displacements. According to this acceptance, plastic behavior of reinforced shear wall occurs when the vertical strain reaches elastic strain limit. In the definition of finite element, displacement functions are chosen considering that the partition of shear walls just at floor levels, are enough for solution. Results of this study are compared with the solution obtained from a different computer programme and experimental results.

Experimental study on the adiabatic shear bands

International Nuclear Information System (INIS)

Affouard, J.

1984-07-01

Four martensitic steels (Z50CDV5 steel, 28CND8 steel, 35NCDV16 steel and 4340 steel) with different hardness between 190 and 600 Hsub(B) (Brinell hardness), have been studied by means of dynamic compressive tests on split Hopkinson pressure bar. Microscopic observations show that the fracture are associated to the development of adiabatic shear bands (except 4340 steel with 190 Hsub(B) hardness). By means of tests for which the deformation is stopped at predetermined levels, the measurement of shear and hardness inside the band and the matrix indicates the chronology of this phenomenon: first the localization of shear, followed by the formation of adiabatic shear band and ultimatly crack initiation and propagation. These results correlated with few simulations by finite elements have permitted to suggest two mecanisms of deformation leading to the formation of adiabatic shear bands in this specific test [fr

Shearing single crystal magnesium in the close-packed basal plane at different temperatures

Science.gov (United States)

Han, Ming; Li, Lili; Zhao, Guangming

2018-05-01

Shear behaviors of single crystal magnesium (Mg) in close-packed (0001) basal plane along the [ 1 bar 2 1 bar 0 ], [ 1 2 bar 10 ], [ 10 1 bar 0 ] and [ 1 bar 010 ] directions were studied using molecular dynamics simulations via EAM potential. The results show that both shear stress-strain curves along the four directions and the motion path of free atoms during shearing behave periodic characteristics. It reveals that the periodic shear displacement is inherently related to the crystallographic orientation in single crystal Mg. Moreover, different temperatures in a range from 10 to 750 K were considered, demonstrating that shear modulus decreases with increasing temperatures. The results agree well with the MTS model. It is manifested that the modulus is independent with the shear direction and the size of the atomic model. This work also demonstrates that the classical description of shear modulus is still effective at the nanoscale.

Mean E×B shear effect on geodesic acoustic modes in Tokamaks

International Nuclear Information System (INIS)

Singh, Rameswar; Gurcan, Ozgur D.

2015-01-01

E × B shearing effect on geodesic acoustic mode (GAM) is investigated for the first time both as an initial value problem in the shearing frame and as an eigenvalue value problem in the lab frame. The nontrivial effects are that E × B shearing couples the standard GAM perturbations to their complimentary poloidal parities. The resulting GAM acquires an effective inertia increasing in time leading to GAM damping. Eigenmode analysis shows that GAMs are radially localized by E × B shearing with the mode width being inversely proportional and radial wave number directly proportional to the shearing rate for weak shear. (author)

Noninvasive Localization of Accessory Pathways in Patients with Wolff-Parkinson-White Syndrome: A Strain Imaging Study

Science.gov (United States)

Esmaeilzadeh, Maryam; Omran, Mohammad Taghi Salehi; Maleki, Majid; Haghjoo, Majid; Noohi, Feridoun; Haghighi, Zahra Ojaghi; Sadeghpour, Anita; Davari, Paridokht Nakhostin; Abkenar, Hooman Bakhshandeh

2013-01-01

Background: Noninvasive techniques for the localization of the accessory pathways (APs) might help guide mapping procedures and ablation techniques. We sought to examine the diagnostic accuracy of strain imaging for the localization of the APs in Wolff-Parkinson-White syndrome. Methods: We prospectively studied 25 patients (mean age = 32 ± 17 years, 58.3% men) with evidence of pre-excitation on electrocardiography (ECG). Electromechanical interval was defined as the time difference between the onset of delta wave and the onset of regional myocardial contraction. Time differences between the onset of delta wave (δ) and the onset of regional myocardial contraction (δ-So), peak systolic motion (δ-Sm), regional strain (δ-ε), peak strain (δ-εp), and peak strain rate (δ-SRp) were measured. Results: There was a significant difference between time to onset of delta wave to onset of peak systolic motion (mean ± SD) in the AP location (A) and normal segments (B) versus that in the normal volunteers (C) [A: (57.08 ± 23.88 msec) vs. B: (75.20 ± 14.75) vs. C: (72.9 0 ± 11.16); p value (A vs. B) = 0.004 and p value (A vs. C) = 0.18] and [A: (49.17 ± 35.79) vs. B: (67.60 ± 14.51) vs. C: (67.40 ± 6.06 msec); p value (A vs. B) < 0.001 and p value (A vs. C) = 0.12, respectively]. Conclusion: Our study showed that strain imaging parameters [(δ-So) and (δ-Strain)] are superior to the ECG in the localization of the APs (84% vs. 76%). PMID:23967027

Evaluation of local deformation behavior accompanying fatigue damage in F82H welded joint specimens by using digital image correlation

International Nuclear Information System (INIS)

Nakata, Toshiya; Tanigawa, Hiroyasu

2012-01-01

Highlights: ► In tensile, the TIG welded joint material was concentrated in the THAZ. ► In tensile, fracture occurred at the point where the axial strain converged. ► In fatigue, fracture occurred at the point where the Max. shear strain converged. ► Many macrocracks and cavities formed in the FGHAZ and THAZ of the cross section. - Abstract: By using digital image correlation, the deformation behaviors of local domains of F82H joint specimens welded using tungsten inert gas (TIG) and electron beam (EB) welding were evaluated during tensile and fatigue testing. In the tensile test specimens, the tensile strength decreased in the TIG-welded joints, and ductility decreased in both the EB- and TIG-welded joints. Because axial strain increased in the tempered heat-affected zone (HAZ) and led to the fracture of the TIG-welded joint, the strength was considered to have decreased because of welding. In fatigue testing, the number of cycles to fracture for the welded joint decreased to less than 40–60% of that for the base metal. For both fracture specimens, the largest value of shear strain was observed in the region approximately between the fine-grained HAZ and tempered HAZ; this shear strain ultimately led to fracture. Cavities and macrocracks were observed in the fine-grained HAZ and tempered HAZ in the cross sections of the fracture specimens, and geometrical damage possibly resulted in the reduction of fatigue lifetime.

Shear strength characteristics of mechanically biologically treated municipal solid waste (MBT-MSW) from Bangalore

International Nuclear Information System (INIS)

Sivakumar Babu, G.L.; Lakshmikanthan, P.; Santhosh, L.G.

2015-01-01

Highlights: • Shear strength properties of mechanically biologically treated municipal solid waste. • Effect of unit weight and particle size on the shear strength of waste. • Effect of particle size on the strength properties. • Stiffness ratio and the strength ratio of MSW. - Abstract: Strength and stiffness properties of municipal solid waste (MSW) are important in landfill design. This paper presents the results of comprehensive testing of shear strength properties of mechanically biologically treated municipal solid waste (MBT-MSW) in laboratory. Changes in shear strength of MSW as a function of unit weight and particle size were investigated by performing laboratory studies on the MSW collected from Mavallipura landfill site in Bangalore. Direct shear tests, small scale and large scale consolidated undrained and drained triaxial tests were conducted on reconstituted compost reject MSW samples. The triaxial test results showed that the MSW samples exhibited a strain-hardening behaviour and the strength of MSW increased with increase in unit weight. Consolidated drained tests showed that the mobilized shear strength of the MSW increased by 40% for a unit weight increase from 7.3 kN/m 3 to 10.3 kN/m 3 at 20% strain levels. The mobilized cohesion and friction angle ranged from 5 to 9 kPa and 8° to 33° corresponding to a strain level of 20%. The consolidated undrained tests exhibited reduced friction angle values compared to the consolidated drained tests. The friction angle increased with increase in the unit weight from 8° to 55° in the consolidated undrained tests. Minor variations were found in the cohesion values. Relationships for strength and stiffness of MSW in terms of strength and stiffness ratios are developed and discussed. The stiffness ratio and the strength ratio of MSW were found to be 10 and 0.43

Shear strength characteristics of mechanically biologically treated municipal solid waste (MBT-MSW) from Bangalore

Energy Technology Data Exchange (ETDEWEB)

Sivakumar Babu, G.L., E-mail: gls@civil.iisc.ernet.in [Department of Civil Engineering, Indian Institute of Science, Bangalore 560012 (India); Lakshmikanthan, P., E-mail: lakshmikanthancp@gmail.com [Centre for Sustainable Technologies (CST), Indian Institute of Science, Bangalore 560012 (India); Santhosh, L.G., E-mail: lgsanthu2006@gmail.com [Centre for Sustainable Technologies (CST), Indian Institute of Science, Bangalore 560012 (India)

2015-05-15

Highlights: • Shear strength properties of mechanically biologically treated municipal solid waste. • Effect of unit weight and particle size on the shear strength of waste. • Effect of particle size on the strength properties. • Stiffness ratio and the strength ratio of MSW. - Abstract: Strength and stiffness properties of municipal solid waste (MSW) are important in landfill design. This paper presents the results of comprehensive testing of shear strength properties of mechanically biologically treated municipal solid waste (MBT-MSW) in laboratory. Changes in shear strength of MSW as a function of unit weight and particle size were investigated by performing laboratory studies on the MSW collected from Mavallipura landfill site in Bangalore. Direct shear tests, small scale and large scale consolidated undrained and drained triaxial tests were conducted on reconstituted compost reject MSW samples. The triaxial test results showed that the MSW samples exhibited a strain-hardening behaviour and the strength of MSW increased with increase in unit weight. Consolidated drained tests showed that the mobilized shear strength of the MSW increased by 40% for a unit weight increase from 7.3 kN/m{sup 3} to 10.3 kN/m{sup 3} at 20% strain levels. The mobilized cohesion and friction angle ranged from 5 to 9 kPa and 8° to 33° corresponding to a strain level of 20%. The consolidated undrained tests exhibited reduced friction angle values compared to the consolidated drained tests. The friction angle increased with increase in the unit weight from 8° to 55° in the consolidated undrained tests. Minor variations were found in the cohesion values. Relationships for strength and stiffness of MSW in terms of strength and stiffness ratios are developed and discussed. The stiffness ratio and the strength ratio of MSW were found to be 10 and 0.43.

Translation vs. Rotation: The Battle for Accommodation of Dextral Shear at the Northern Terminus of the Central Walker Lane, Western Nevada

Science.gov (United States)

Carlson, C. W.; Faulds, J. E.

2014-12-01

Positioned between the Sierra Nevada microplate and Basin and Range in western North America, the Walker Lane (WL) accommodates ~20% of the dextral motion between the North American and Pacific plates on predominately NW-striking dextral and ENE to E-W-striking sinistral fault systems. The Terrill Mountains (TM) lie at the northern terminus of a domain of dextral faults accommodating translation of crustal-blocks in the central WL and at the southeast edge of sinistral faults accommodating oroclinal flexure and CW rotation of blocks in the northern WL. As the mechanisms of strain transfer between these disparate fault systems are poorly understood, the thick Oligocene to Pliocene volcanic strata of the TM area make it an ideal site for studying the transfer of strain between regions undergoing differing styles of deformation and yet both accommodating dextral shear. Detailed geologic mapping and paleomagnetic study of ash-flow tuffs in the TM region has been conducted to elucidate Neogene strain accommodation for this transitional region of the WL. Strain at the northernmost TM appears to be transferred from a system of NW-striking dextral faults to a system of ~E-W striking sinistral faults with associated CW flexure. A distinct ~23 Ma paleosol is locally preserved below the tuff of Toiyabe and provides an important marker bed. This paleosol is offset with ~6 km of dextral separation across the fault bounding the NE flank of the TM. This fault is inferred as the northernmost strand of the NW-striking, dextral Benton Spring fault system, with offset consistent with minimums constrained to the south (6.4-9.6 km, Gabbs Valley Range). Paleomagnetic results suggest counter-intuitive CCW vertical-axis rotation of crustal blocks south of the domain boundary in the system of NW-striking dextral faults, similar to some other domains of NW-striking dextral faults in the northern WL. This may result from coeval dextral shear and WNW-directed extension within the left

Internal shear cracking in bulk metal forming

DEFF Research Database (Denmark)

Christiansen, Peter; Nielsen, Chris Valentin; Bay, Niels Oluf

2017-01-01

This paper presents an uncoupled ductile damage criterion for modelling the opening and propagation of internal shear cracks in bulk metal forming. The criterion is built upon the original work on the motion of a hole subjected to shear with superimposed tensile stress triaxiality and its overall...... performance is evaluated by means of side-pressing formability tests in Aluminium AA2007-T6 subjected to different levels of pre-strain. Results show that the new proposed criterionis able to combine simplicity with efficiency for predicting the onset of fracture and the crack propagation path for the entire...... cracking to internal cracks formed undert hree-dimensional states of stress that are typical of bulk metal forming....

Squatting-Related Tibiofemoral Shear Reaction Forces and a Biomechanical Rationale for Femoral Component Loosening

Directory of Open Access Journals (Sweden)

Ashvin Thambyah

2014-01-01

Full Text Available Previous gait studies on squatting have described a rapid reversal in the direction of the tibiofemoral joint shear reaction force when going into a full weight-bearing deep knee flexion squat. The effects of such a shear reversal have not been considered with regard to the loading demand on knee implants in patients whose activities of daily living require frequent squatting. In this paper, the shear reversal effect is discussed and simulated in a finite element knee implant-bone model, to evaluate the possible biomechanical significance of this effect on femoral component loosening of high flexion implants as reported in the literature. The analysis shows that one of the effects of the shear reversal was a switch between large compressive and large tensile principal strains, from knee extension to flexion, respectively, in the region of the anterior flange of the femoral component. Together with the known material limits of cement and bone, this large mismatch in strains as a function of knee position provides new insight into how and why knee implants may fail in patients who perform frequent squatting.

Microstructural and Mechanical Property Characterization of Shear Formed Aerospace Aluminum Alloys

Science.gov (United States)

Troeger, Lillianne P.; Domack, Marcia S.; Wagner, John A.

2000-01-01

Advanced manufacturing processes such as near-net-shape forming can reduce production costs and increase the reliability of launch vehicle and airframe structural components through the reduction of material scrap and part count and the minimization of joints. The current research is an investigation of the processing-microstructure-property relationships for shear formed cylinders of the Al-Cu-Li-Mg-Ag alloy 2195 for space applications and the Al-Cu-Mg-Ag alloy C415 for airframe applications. Cylinders which had undergone various amounts of shear-forming strain were studied to correlate the grain structure, texture, and mechanical properties developed during and after shear forming.

Design and implementation of a shearing apparatus for the experimental study of shear displacement in rocks

Science.gov (United States)

Moore, Johnathan; Crandall, Dustin; Gill, Magdalena; Brown, Sarah; Tennant, Bryan

2018-04-01

Fluid flow in the subsurface is not well understood in the context of "impermeable" geologic media. This is especially true of formations that have undergone significant stress fluctuations due to injection or withdrawal of fluids that alters the localized pressure regime. When the pressure regime is altered, these formations, which are often already fractured, move via shear to reduce the imbalance in the stress state. While this process is known to happen, the evolution of these fractures and their effects on fluid transport are still relatively unknown. Numerous simulation and several experimental studies have been performed that characterize the relationship between shearing and permeability in fractures; while many of these studies utilize measurements of fluid flow or the starting and ending geometries of the fracture to characterize shear, they do not characterize the intermediate stages during shear. We present an experimental apparatus based on slight modifications to a commonly available Hassler core holder that allows for shearing of rocks, while measuring the hydraulic and mechanical changes to geomaterials during intermediate steps. The core holder modification employs the use of semi-circular end caps and structural supports for the confining membrane that allow for free movement of the sheared material while preventing membrane collapse. By integrating this modified core holder with a computed tomography scanner, we show a new methodology for understanding the interdependent behavior between fracture structure and flow properties during intermediate steps in shearing. We include a case study of this device function which is shown here through shearing of a fractured shale core and simultaneous observation of the mechanical changes and evolution of the hydraulic properties during shearing.

The roles of electric field shear and Shafranov shift in sustaining high confinement in enhanced reversed shear plasmas on the TFTR tokamak

International Nuclear Information System (INIS)

Synakowski, E.J.; Beer, M.A.

1997-02-01

The relaxation of core transport barriers in TFTR Enhanced Reversed Shear plasmas has been studied by varying the radial electric field using different applied torques from neutral beam injection. Transport rates and fluctuations remain low over a wide range of radial electric field shear, but increase when the local E x B shearing rates are driven below a threshold comparable to the fastest linear growth rates of the dominant instabilities. Shafranov-shift-induced stabilization alone is not able to sustain enhanced confinement

Mechanical Characterization of Immature Porcine Brainstem in Tension at Dynamic Strain Rates.

Science.gov (United States)

Zhao, Hui; Yin, Zhiyong; Li, Kui; Liao, Zhikang; Xiang, Hongyi; Zhu, Feng

2016-01-21

Many brain injury cases involve pediatric road traffic accidents, and among these, brainstem injury causes disastrous outcomes. A thorough understanding of the tensile characterization of immature brainstem tissue is crucial in modeling traumatic brain injury sustained by children, but limited experimental data in tension is available for the immature brain tissue at dynamic strain rates. We harvested brainstem tissue from immature pigs (about 4 weeks old, and at a developmental stage similar to that of human toddlers) as a byproduct from a local slaughter house and very carefully prepared the samples. Tensile tests were performed on specimens at dynamic strain rates of 2/s, 20/s, and 100/s using a biological material instrument. The constitutive models, Fung, Ogden, Gent, and exponential function, for immature brainstem tissue material property were developed for the recorded experimental data using OriginPro 8.0 software. The t test was performed for infinitesimal shear modules. The curves of stress-versus-stretch ratio were convex in shape, and inflection points were found in all the test groups at the strain of about 2.5%. The average Lagrange stress of the immature brainstem specimen at the 30% strain at the strain rates of 2, 20, and 100/s was 273±114, 515±107, and 1121±197 Pa, respectively. The adjusted R-Square (R2) of Fung, Ogden, Gent, and exponential model was 0.820≤R2≤0.933, 0.774≤R2≤0.940, 0.650≤R2≤0.922, and 0.852≤R2≤0.981, respectively. The infinitesimal shear modulus of the strain energy functions showed a significant association with the strain rate (pmaterial in dynamic tensile tests, and the tissue becomes stiffer with increased strain rate. The reported results may be useful in the study of brain injuries in children who sustain injuries in road traffic accidents. Further research in more detail should be performed in the future.

Effect of strain and deformation route on grain boundary characteristics and recrystallization behavior of aluminum

International Nuclear Information System (INIS)

Sakai, Tetsuo; Takahashi, Yasuo; Utsunomiya, Hiroshi

2014-01-01

The effect of strain and deformation route on the recrystallization behavior of aluminum sheets has been investigated using well lubricated cold rolling and continuous equal channel angular extrusion. Three different deformation routes in plane strain corresponding to (1) simple shear, (2) compression, and (3) the combination of simple shear and compression were performed on 1100 aluminum sheet. Fixed amounts of the equivalent strain of 1.28 and 1.06 were accumulated in each route. In case of the combined deformation route, the ratio of shear strain to the total equivalent strain was varied. The recrystallized grain size was finer if the combined deformation route was employed instead of the monotonic route under the same amount of equivalent strain at either strain level. The density of high angle grain boundaries that act as nucleation sites for recrystallization was higher in materials deformed by the combined route. The orientation imaging micrographs revealed that the change in deformation route is effective for introducing a larger number of new high angle grain boundaries with relatively low misorientation angle

Effect of strain and deformation route on grain boundary characteristics and recrystallization behavior of aluminum

Science.gov (United States)

Sakai, Tetsuo; Utsunomiya, Hiroshi; Takahashi, Yasuo

2014-08-01

The effect of strain and deformation route on the recrystallization behavior of aluminum sheets has been investigated using well lubricated cold rolling and continuous equal channel angular extrusion. Three different deformation routes in plane strain corresponding to (1) simple shear, (2) compression, and (3) the combination of simple shear and compression were performed on 1100 aluminum sheet. Fixed amounts of the equivalent strain of 1.28 and 1.06 were accumulated in each route. In case of the combined deformation route, the ratio of shear strain to the total equivalent strain was varied. The recrystallized grain size was finer if the combined deformation route was employed instead of the monotonic route under the same amount of equivalent strain at either strain level. The density of high angle grain boundaries that act as nucleation sites for recrystallization was higher in materials deformed by the combined route. The orientation imaging micrographs revealed that the change in deformation route is effective for introducing a larger number of new high angle grain boundaries with relatively low misorientation angle.

Controlling microstructure and texture in magnesium alloy sheet by shear-based deformation processing

Science.gov (United States)

Sagapuram, Dinakar

Application of lightweight Mg sheet is limited by its low workability, both in production of sheet (typically by multistep hot and cold-rolling) and forming of sheet into components. Large strain extrusion machining (LSEM), a constrained chip formation process, is used to create Mg alloy AZ31B sheet in a single deformation step. The deformation in LSEM is shown to be intense simple shear that is confined to a narrow zone, which results in significant deformation-induced heating up to ~ 200°C and reduces the need for pre-heating to realize continuous sheet forms. This study focuses on the texture and microstructure development in the sheet processed by LSEM. Interestingly, deep, highly twinned steady-state layer develops in the workpiece subsurface due to the compressive field ahead of the shear zone. The shear deformation, in conjunction with this pre-deformed twinned layer, results in tilted-basal textures in the sheet with basal planes tilted well away from the surface. These textures are significantly different from those in rolled sheet, where basal planes are nearly parallel to the surface. By controlling the strain path, the basal plane inclination from the surface could be varied in the range of 32-53°. B-fiber (basal plane parallel to LSEM shear plane), associated with basal slip, is the major texture component in the sheet. An additional minor C2-fiber component appears above 250°C due to the thermal activation of pyramidal slip. Together with these textures, microstructure ranges from severely cold-worked to (dynamically) recrystallized type, with the corresponding grain sizes varying from ultrafine- (~ 200 nm) to fine- (2 mum) grained. Small-scale limiting dome height (LDH) confirmed enhanced formability (~ 50% increase in LDH) of LSEM sheet over the conventional rolled sheet. Premature, twinning-driven shear fractures are observed in the rolled sheet with the basal texture. In contrast, LSEM sheet with a tilted-basal texture favorably oriented for

Localized microjetting in the collapse of surface macrocavities

Science.gov (United States)

Olney, K. L.; Chiu, P.-H.; Benson, D. J.; Higgins, A.; Serge, M.; Nesterenko, V. F.

2015-02-01

This paper focuses on the multiscale mechanism of collapse of hemicylindrical annular surface macrocavities in steel caused by high-strain, high-strain rate plastic flow of copper. Experiments and simulations revealed that a two-stage process is responsible for the observed microjetting phenomena: the formation of lateral copper microjets from the localized shear flow in copper at the interface during the filling of the cavity, and their subsequent collision at the apex of the macrocavity generating two additional horizontal microjets. The lengths of these microjets were an order of magnitude smaller than the cavity size but linearly scaled with the cavity radius. This process of microjet development is sensitive to the cavity geometry and is unlike the previously observed jetting phenomena in cavitation, impact crater collapse, or shock-induced cavity collapse.

Monotonic and cyclic responses of impact polypropylene and continuous glass fiber-reinforced impact polypropylene composites at different strain rates

KAUST Repository

Yudhanto, Arief

2016-03-08

Impact copolymer polypropylene (IPP), a blend of isotactic polypropylene and ethylene-propylene rubber, and its continuous glass fiber composite form (glass fiber-reinforced impact polypropylene, GFIPP) are promising materials for impact-prone automotive structures. However, basic mechanical properties and corresponding damage of IPP and GFIPP at different rates, which are of keen interest in the material development stage and numerical tool validation, have not been reported. Here, we applied monotonic and cyclic tensile loads to IPP and GFIPP at different strain rates (0.001/s, 0.01/s and 0.1/s) to study the mechanical properties, failure modes and the damage parameters. We used monotonic and cyclic tests to obtain mechanical properties and define damage parameters, respectively. We also used scanning electron microscopy (SEM) images to visualize the failure mode. We found that IPP generally exhibits brittle fracture (with relatively low failure strain of 2.69-3.74%) and viscoelastic-viscoplastic behavior. GFIPP [90]8 is generally insensitive to strain rate due to localized damage initiation mostly in the matrix phase leading to catastrophic transverse failure. In contrast, GFIPP [±45]s is sensitive to the strain rate as indicated by the change in shear modulus, shear strength and failure mode.

3D finite element analysis of stress distributions and strain energy release rates for adhesive bonded flat composite lap shear joints having pre-existing delaminations

Energy Technology Data Exchange (ETDEWEB)

Parida, S. K.; Pradhan, A. K. [Indian Institute of Technology, Bhubaneswar (India)

2014-02-15

The rate of propagation of embedded delamination in the strap adherend of lap shear joint (LSJ) made of carbon/epoxy composites has been evaluated employing three-dimensional non-linear finite elements. The delamination has been presumed to pre-exist in the thin resin layer between the first and second plies of the strap adherend. The inter-laminar peel and shear stress distributions have been studied in details and are seen to be predominantly three-dimensional in nature. The components of strain energy release rate (SERR) corresponding to the opening, sliding and cross sliding modes of delamination are significantly different at the two fronts of the embedded delamination. The sequential release of multi-point constraint (MPC) finite elements in the vicinity of the delamination fronts enables to simulate the growth of the delamination at either ends. This simulation procedure can be utilized effectively for evaluation of the status of the structural integrity of the bonded joints.

Piezoelectric energy harvesting through shear mode operation

International Nuclear Information System (INIS)

Malakooti, Mohammad H; Sodano, Henry A

2015-01-01

Piezoelectric materials are excellent candidates for use in energy harvesting applications due to their high electromechanical coupling properties that enable them to convert input mechanical energy into useful electric power. The electromechanical coupling coefficient of the piezoelectric material is one of the most significant parameters affecting energy conversion and is dependent on the piezoelectric mode of operation. In most piezoceramics, the d 15 piezoelectric shear coefficient is the highest coefficient compared to the commonly used axial and transverse modes that utilize the d 33 and the d 31 piezoelectric strain coefficients. However, complicated electroding methods and challenges in evaluating the performance of energy harvesting devices operating in the shear mode have slowed research in this area. The shear deformation of a piezoelectric layer can be induced in a vibrating sandwich beam with a piezoelectric core. Here, a model based on Timoshenko beam theory is developed to predict the electric power output from a cantilever piezoelectric sandwich beam under base excitations. It is shown that the energy harvester operating in the shear mode is able to generate ∼50% more power compared to the transverse mode for a numerical case study. Reduced models of both shear and transverse energy harvesters are obtained to determine the optimal load resistance in the system and perform an efficiency comparison between two models with fixed and adaptive resistances. (paper)

Action-at-a-distance metamaterials: Distributed local actuation through far-field global forces

Science.gov (United States)

Hedayati, R.; Mirzaali, M. J.; Vergani, L.; Zadpoor, A. A.

2018-03-01

Mechanical metamaterials are a sub-category of designer materials where the geometry of the material at the small-scale is rationally designed to give rise to unusual properties and functionalities. Here, we propose the concept of "action-at-a-distance" metamaterials where a specific pattern of local deformation is programmed into the fabric of (cellular) materials. The desired pattern of local actuation could then be achieved simply through the application of one single global and far-field force. We proposed graded designs of auxetic and conventional unit cells with changing Poisson's ratios as a way of making "action-at-a-distance" metamaterials. We explored five types of graded designs including linear, two types of radial gradients, checkered, and striped. Specimens were fabricated with indirect additive manufacturing and tested under compression, tension, and shear. Full-field strain maps measured with digital image correlation confirmed different patterns of local actuation under similar far-field strains. These materials have potential applications in soft (wearable) robotics and exosuits.

The brittle-viscous-plastic evolution of shear bands in the South Armorican Shear Zone

Science.gov (United States)

Bukovská, Zita; Jeřábek, Petr; Morales, Luiz F. G.; Lexa, Ondrej; Milke, Ralf

2014-05-01

Shear bands are microscale shear zones that obliquely crosscut an existing anisotropy such as a foliation. The resulting S-C fabrics are characterized by angles lower than 45° and the C plane parallel to shear zone boundaries. The S-C fabrics typically occur in granitoids deformed at greenschist facies conditions in the vicinity of major shear zones. Despite their long recognition, mechanical reasons for localization of deformation into shear bands and their evolution is still poorly understood. In this work we focus on microscale characterization of the shear bands in the South Armorican Shear Zone, where the S-C fabrics were first recognized by Berthé et al. (1979). The initiation of shear bands in the right-lateral South Armorican Shear Zone is associated with the occurrence of microcracks crosscutting the recrystallized quartz aggregates that define the S fabric. In more advanced stages of shear band evolution, newly formed dominant K-feldspar, together with plagioclase, muscovite and chlorite occur in the microcracks, and the shear bands start to widen. K-feldspar replaces quartz by progressively bulging into the grain boundaries of recrystallized quartz grains, leading to disintegration of quartz aggregates and formation of fine-grained multiphase matrix mixture. The late stages of shear band development are marked by interconnection of fine-grained white mica into a band that crosscuts the original shear band matrix. In its extremity, the shear band widening may lead to the formation of ultramylonites. With the increasing proportion of shear band matrix from ~1% to ~12%, the angular relationship between S and C fabrics increases from ~30° to ~40°. The matrix phases within shear bands show differences in chemical composition related to distinct evolutionary stages of shear band formation. The chemical evolution is well documented in K-feldspar, where the albite component is highest in porphyroclasts within S fabric, lower in the newly formed grains within

"Virtual shear box" experiments of stress and slip cycling within a subduction interface mélange